Hack: Originally this word meant to quickly write a software program for a limited purpose though it evolved to mean the study and writing of innovative software programs. Increasingly the term is used by civilians to mean breaking into computer systems for malicious purposes – a practice more properly referred to as cracking. The word is also used as a noun to mean a clever piece of programming.

ICQ. (I seek you): A subnetwork of the Internet similar to the IRC but devoted to private conversations. Similar to instant messaging.

IRC (Internet Relay Chat): A popular subnetwork of the Internet, in which a number of participants can have real-time conversations in online chat rooms devoted to specific interests.

.JPG (or.jpeg for joint photographers experts group): A format for digitizing, compressing and storing pictures on computers. Pictures in such formats are designated by the extension.jpg after the file name.

Kludge: A quickly written, often improvised, software program that serves a particular purpose, often intended to fix a bug or remedy some other setback in computer operations.

Machine: A computer.

MUD (Multiuser Domain, Multiuser Dimension or Multiuser Dungeons): A subnetwork related to the IRC in which participants play real-time games or engage in simulated activities.

MUDhead: One who participates in MUDs.

Packet: A small string of digitized data. All information transmitted over the Internet – e-mail, text, music, pictures, graphics, sounds – is broken down into packets, which are then reassembled at the recipient's end into a usable form.

Packet-Sniffer: A program loaded on a computer router, server or individual computer to divert packets to a third-party's computer, usually for the purpose of illicitly reading a user's messages or learning passcodes and other information.