If you don't find the definition you want here, there are several excellent dictionaries of technical and computer-related terms on the web. You are certainly welcome to ask me about any terms or technical concepts you don't understand, as well. While some of these definitions may seem obvious, some people have expressed confusion as to exactly what they mean.

Ad Hominem
Rejection of a claim or argument on the basis of some irrelevant fact about the author of or the person presenting the claim or argument. See Dr. Michael C. Labossiere's excellent description for further information.

Anonymous remailers
Systems that permit users to send, and sometimes to receive, email while hiding the user's identity. Some also permit anonymous posting to newsgroups. The administrators of such systems either do not keep access logs, or deliberately configure their system so as to make it difficult to determine the identity of the user sending the email or newsgroup messages. Anonymous remailers do have legitimate uses, such as providing a safe way for victims of abuse to participate in support forums without revealing their identity. Unfortunately, they have far more less legitimate uses, and from what I've seen 99% of the use of these services is for illegal or abusive activity. The headers of almost any message posted through an anonymous remailer will give you instructions on who to contact regarding abuse of the service.

Autoresponder
A script that sends out a standard response whenever email is sent to a particular email address.

BBS
Acronym for bulletin board system. They are usually message databases where people can log in and leave messages on message boards grouped by topic for any user to see, or private messages for a particular user or users. They often have areas for exchanging files, as well (programs, pictures, etc.) Now that so many people have internet access many BBSs have shut down or fallen into disuse.

Cancelled
Newsgroup messages can be cancelled by issuing messages to the special newsgroup control.cancel. The user who cancels the message is supposed to be the same as the user who posted the message, but it only takes a couple of seconds changing a few settings in your news reading software to impersonate the poster well enough to cancel the messages (forge-cancel). Some news servers don't honor cancel messages, and if the message has already been archived by a service like DejaNews the cancellation would remove it from the archives. See the Cancel FAQ for more information.

Crack, cracker
The act of forcibly breaking the security on a system, or using programming skills to act maliciously. Crackers are considered a lower life form by most hackers.

Defamation
An attack on the good reputation of a person, by slander or libel. (Duhaime's Law Dictionary)

Email
Messages sent from one internet user to another, usually private, unlike newsgroup posts. Most email can be traced back to the sender by examining the headers of the message, which shows the system at which the message originated and any systems it passed through between that system and the recipient's system. The administrators of the originating system can determine the identity of the user from those headers, if their system is configured properly and they keep normal system access logs.

Finger, .plan/.project
A Unix utility that reports information about other users who have accounts on Unix machines. Since the internet is largely built on computers running various versions of Unix, you can often finger someone's email address and find out, for example, where and when a person last logged in to the system. If that person has created special files called .plan or .project you can read the contents of those files. Some system administrators disable the finger command on their machines because of security problems associated with it. Here's a web-based finger gateway if you want to try the finger command.

Flame
A flame is usually a message that is extremely critical, and often irrational, of someone or something. Sometimes flames are intentionally trying to start a flame war—a series of many messages with people essentially yelling at each other. Such deliberately provocative messages are often called trolls (the same term is used for those who post them). Flame wars are extremely common, and if you've been active on Usenet for any time at all you've probably been involved in one. Anyone who expresses any strong opinions is generally considered fair game by flamers, so don't take it personally—consider it a compliment that you are, at least, making an impression.

Gateway
A network point that acts as an entrance to another network, such as the server through which people on a company's local area network access the internet. Often a gateway conceals the IP address of the specific user sending out information, and outsiders can only see the IP address of the gateway itself.

Hacker
Hackers are those who enjoy delving deep into a subject rather than learning just the minimum needed to get by. Usually used to refer to programmers.

Harassment
The legal definition of harassment is "a course of conduct directed at a specific person that causes substantial emotional distress in such person and serves no legitimate purpose" or "words, gestures, and actions which tend to annoy, alarm and abuse (verbally) another person." (Black's Law Dictionary 717, 6th ed. 1990)

Harassing phone calls
Georgia law 46-5-21 G says:
  1. It shall be a misdemeanor for any person, by means of telephone communication in this state, to:
    1. Make any comment, request, suggestion, or proposal which is obscene, lewd, lascivious, filthy, or indecent;
    2. Make a telephone call, whether or not conversation ensues, without disclosing his identity and with intent to annoy, abuse, threaten, or harass any person at the called number;
    3. Make or cause the telephone of another repeatedly or continuously to ring, with intent to harass any person at the called number; or
    4. Make repeated telephone calls, during which conversation ensues, solely to harass any person at the called number.
  2. Any person who knowingly permits any telephone under his control to be used for any purpose prohibited by this Code section shall be guilty of a misdemeanor.

Internet
A network of many computers connected via telecommunication networks. The computers communicate using a set of protocols called TCP/IP (Transmission Control Protocol/Internet Protocol).

IP address
Every user on a TCP/IP system has to be assigned a unique identifier called an IP address. Because there are a limited number of acceptable addresses, most ISPs now assign an address from the pool they're permitted to use randomly to each user as the user calls in to connect to the system—dynamic IP addressing There was a time, though, when most ISPs permanently assigned one IP address to each of their users (fixed IP addressing), and you could identify that user by checking the headers of his newsgroup and email messages for that address. For instance, my IP address was once 168.121.39.219 and you could find that in any post I made during that period. Hillyard's was 168.121.127.70 while he was a MindSpring user.

ISP
Acronym for internet service provider. An organization through which you gain access to the internet.

Libel
Defamation by writing such as in a newspaper or a letter. (Duhaime's Law Dictionary)

Georgia Code 51-5-1 G states:
  1. A libel is a false and malicious defamation of another, expressed in print, writing, pictures, or signs, tending to injure the reputation of the person and exposing him to public hatred, contempt, or ridicule.
  2. The publication of the libelous matter is essential to recovery.
Section 51-5-3 further says:
A libel is published as soon as it is communicated to any person other than the party libeled.

Mailbomb
A mailbomb is an attempt to send so much mail to a mailbox (email address) to make that mailbox overloaded or inaccessible, or to even crash the machine (server) on which that mailbox resides. You can learn more in the Email Abuse FAQ.

MLM
Acronym for multi-level marketing. From The Federal Trade Commission's website:"
MLM - also known as "network" or "matrix" marketing - is a way of selling goods and services through distributors. These plans typically promise that people who sign up as distributors will get commissions two ways - on their own sales and on the sales their recruits have made.

Pyramid schemes - a form of multi-level marketing - involve paying commissions to distributors only for recruiting new distributors. Pyramid schemes are illegal in most states because the plans inevitably collapse when no new distributors can be recruited. When a plan collapses, most people - except those at the top of the pyramid - lose their money.

MLMs should pay commissions for the retail sales of goods or services, not for recruiting new distributors. MLMs that involve the sale of business opportunities or franchises, as defined by the Franchise Rule, must comply with the Rule's requirements about disclosing the number and percentage of existing franchisees who have achieved the claimed results, as well as cautionary language.
Newsgroup, Usenet
Usenet is the name for many discussion forums (newsgroups) that are normally open to any internet user whose internet provider carries them. You can post new messages, read what others have posted, and reply to those posts. The distribution of some newsgroups is limited—for instance, at one time MindSpring maintained 113 newsgroups which could only be accessed by users on their own system. If you have ever used the message boards on bulletin board systems or in AOL's forums, it's the same concept. Most newsgroup posts can easily be traced to the originating system and user by examining the headers, which show where the message originated and what systems it went through between there and the reader's system. The administrators of the originating system can determine the identity of the user from those headers, if their system is configured properly and they keep normal system access logs.

Occam's Razor
Originally propounded by the English philospher, William of Occam (1300-1349), as:
Entia non sunt multiplicanda praeter necessitatem.
Which is translated:
Entities should not be multiplied more than necessary.
In other words, the simplest explanation is the one that is most likely to be correct, or KISS (keep it simple, stupid!) Occam's Razor is often mentioned in Robert Heinlein's works.

Online service provider
I'm going to call these OSPs for short. They're companies like AOL, CompuServe and Prodigy that provide proprietary content and services accessible only to their members, and require that members use their own proprietary software to access their services. Many of them provide internet access, as well, but they aren't ISPs.

Packet
A unit of data sent across a network. When a large block of data is to be sent over a network, it is broken up into several packets, sent, and the reassembled at the other end. Packets often include checksum codes to detect transmission errors. The exact layout of an individual packet is determined by the protocol being used.

Packet Sniffer
A program which displays the contents of all packets passing through a network connection—you might think of it as a wire tap for computers.

Pedophile
Pervert who is sexually attracted to children.

Point of Presence (PoP)
Definition from the Free On-line Dictionary of Computing:
(PoP) A site where there exists a collection of telecommunications equipment, usually modems, digital leased lines and multi-protocol routers. An Internet access provider may operate several PoPs distributed throughout their area of operation to increase the chance that their subscribers will be able to reach one with a local telephone call. The alternative is for them to use virtual PoPs (virtual points of presence) via some third party.

.sig file, .sig line
Text often inserted at the end of a user's posts, usually with that person's name, email address and maybe a web site URL, and often including a quote of some sort. Most email and newsreader programs can be set to automatically insert the .sig line at the end of every message without the user's intervention.

Simple assault
Georgia code 16-5-20 G states:
  1. A person commits the offense of simple assault when he either:
    1. Attempts to commit a violent injury to the person of another; or
    2. Commits an act which places another in reasonable apprehension of immediately receiving a violent injury.
  2. Except as provided in subsection (c) of this Code section, a person who commits the offense of simple assault shall be guilty of a misdemeanor.
  3. Any person who commits the offense of simple assault in a public transit vehicle or station shall, upon conviction thereof, be punished for a misdemeanor of a high and aggravated nature. For purposes of this Code section, "public transit vehicle" means a bus, van, or rail car used for the transportation of passengers within a system which receives a subsidy from tax revenues or is operated under a franchise contract with a county or municipality of this state.

Slander
Verbal or spoken defamation. (Duhaime's Law Dictionary)

Georgia Code 51-5-4 G states:
  1. Slander or oral defamation consists in:
    1. Imputing to another a crime punishable by law;
    2. Charging a person with having some contagious disorder or with being guilty of some debasing act which may exclude him from society;
    3. Making charges against another in reference to his trade, office, or profession, calculated to injure him therein; or
    4. Uttering any disparaging words productive of special damage which flows naturally therefrom.
  2. In the situation described in paragraph (4) of subsection (a) of this Code section, special damage is essential to support an action; in the situations described in paragraphs (1) through (3) of subsection (a) of this Code section, damage is inferred.

Social engineering
Term used among crackers for exploiting weaknesses in people, rather than software—tricking someone into giving out information like passwords that will compromise system security.
Stalking
Effective July 1, 2000, Georgia code 16-5-90 G says:
    1. A person commits the offense of stalking when he or she follows, places under surveillance, or contacts another person at or about a place or places without the consent of the other person for the purpose of harassing and intimidating the other person. For the purpose of this article, the terms "computer" and "computer network" shall have the same meanings as set out in Code Section 16-9-92; the term "contact" shall mean any communication including without being limited to communication in person, by telephone, by mail, by broadcast, by computer, by computer network, or by any other electronic device; and the place or places that contact by telephone, mail, broadcast, computer, computer network, or any other electronic device is deemed to occur shall be the place or places where such communication is received. For the purpose of this article, the term "place or places" shall include any public or private property occupied by the victim other than the residence of the defendant. For the purposes of this article, the term "harassing and intimidating" means a knowing and willful course of conduct directed at a specific person which causes emotional distress by placing such person in reasonable fear for such person's safety or the safety of a member of his or her immediate family, by establishing a pattern of harassing and intimidating behavior, and which serves no legitimate purpose. This Code section shall not be construed to require that an overt threat of death or bodily injury has been made.
    2. A person commits the offense of stalking when such person, in violation of a bond to keep the peace posted pursuant to Code Section 17-6-110, standing order issued under Code Section 19-1-1, temporary restraining order, temporary protective order, permanent restraining order, permanent protective order, preliminary injunction, or permanent injunction or condition of pretrial release, condition of probation, or condition of parole in effect prohibiting the harassment or intimidation of another person, broadcasts or publishes, including electronic publication, the picture, name, address, or phone number of a person for whose benefit the bond, order, or condition was made and without such person's consent in such a manner that causes other persons to harass or intimidate such person and the person making the broadcast or publication knew or had reason to believe that such broadcast or publication would cause such person to be harassed or intimidated by others.
  1. Except as provided in subsection (c) of this Code section, a person who commits the offense of stalking is guilty of a misdemeanor.
  2. Upon the second conviction, and all subsequent convictions, for stalking, the defendant shall be guilty of a felony and shall be punished by imprisonment for not less than one year nor more than ten years.
  3. Before sentencing a defendant for any conviction of stalking under this Code section or aggravated stalking under Code Section 16-5-91, the sentencing judge may require psychological evaluation of the offender and shall consider the entire criminal record of the offender. At the time of sentencing, the judge is authorized to issue a permanent restraining order against the offender to protect the person stalked and the members of such person's immediate family, and the judge is authorized to require psychological treatment of the offender as a part of the sentence, or as a condition for suspension or stay of sentence, or for probation.
Information about federal stalking laws and laws in other states.

TARDIS
Originally, an acronym for Time And Relative Dimension In Space from the British science fiction series Doctor Who—the Doctor's time machine. The term came into general use among SF fans, then to geeks in general, to refer to any device used for time travel.

Telnet
To communicate with another Internet host using the TELNET (RFC 854) protocol (usually using a program of the same name). Someone logged into his employer's network could, for instance, use the employer's internet gateway to telnet to an account on another system, then send messages through that system to the rest of the internet, in an attempt to hide the origin of the messages.

traceroute
A Unix TCP/IP utility which shows the various machines information goes through before reaching the targeted computer.

Warez
Definition from whatis.com:
Warez (pronounced as though spelled "wares" or possibly by some pronounced like the city of "Juarez") is a term used by software "pirates" to describe software that has been stripped of its copy-protection and made available on the Internet for downloading.