AGP - Accelerated Graphics Port - If you have a separate video card, it probably connects through your motherboard's AGP port (redundant, I know). The brown AGP slot lies directly 'above' the white PCI slots on an ATX form factor motherboard. AGP allows a video card to handle the rendering of 2d and 3d images/video so your CPU can busy itself with other things. Without a separate video card (or crappy onboard video), your CPU is forced to handle the graphics load as well as everything else, which leads to very poor performance in 3d applications.
ANSI - American National Standards Institute - They're responsible for much of the standardization of computer technologies, such as CD-ROM formats. Without standardization, there's no guarantee a CD burnt on one computer could be read by another. And that would be a terrible, terrible thing.
BIOS - Basic Input/Output System - The set of instructions responsible for telling your motherboard how to tell the various devices connected to it work together. Usually stored on a CMOS chip on the motherboard.
CMOS - Complementary Metal Oxide Semiconductor - A type of memory storage that requires very little electrical power to hold data. The BIOS, for example, is stored in this type of memory because the onboard battery will keep it powered for years.
CPU - Central Processing Unit - Also known as the "processor", this device does most of the work and generates most of the heat of the computer. An applied voltage is used to cause cascading changes through millions of transistors (that make up logic gates). The 'speed' of a processor is measured in how many operations (cascading changes) it can do in one second. A typical 'speed' (it's really a frequency, not a speed) is, say, 2.4 GHz, where GHz = gigahertz, or 2.4 billion operations per second.
CRC - Cyclic Redundancy Check - A way of testing whether or not data sent from one place to another arrived intact. The data is separated into chunks, and each chunk is divided by a certain number. The remainder from this division becomes part of the CRC. If the CRCs at either end match, the data send was most likely successful.
CRT - Cathode-Ray Tube - A type of monitor that works on the same principle as a television screen. Beams of electrons (cathode-rays) are fired at a phosphorescent screen, where they excite atoms that discharge optical photons, producing the image you see.
DES - Digital Encryption Standard - A type of encryption that uses only private keys, which the sending and receiver must know. It's so strong that the US government has restricted the exportation of the encryption scheme to other countries. I'd think this reveals a rather high degree of paranoia. The encryption standard is scheduled for replacement by AES (Advanced Encryption Standard), which will probably be easier for the US government to crack, and harder for everyone else.
EIDE - Enhanced IDE - Better than regular IDE. It can handle much larger hard disk drives, supports DMA, and also handles optical drives. If your hard drive is bigger than 528 MB, you definitely have EIDE.
FSB - Front-Side Bus - The physical pathway and interface that exists between the CPU and RAM. Data collected from the RAM must traverse the Front-Side Bus.
FTP - File Transfer Protocol - The protocol responsible for viewing directories and files hosted on a remote computer. It is commonly used to share files across the internet, and can be password-protected.
GUI - Graphical User Interface - It's what you actually look at when you are using your computer. The cursor, icons, windows, folders, and desktop are all part of the GUI. The alternate would be a text-based interface such as Windows 3.1 or UNIX.
HDD - Hard Disk Drive - A type of large-scale, semi-permanent, magnetic storage. Inside, you'll find several stacked platters, each with a stylus (read/write head) hovering above it on a cushion of air, alternately reading from and writing to the surface of the disk.
HTML - HyperText Markup Language - The language a webpage is written in. You can check the HTML source of a page by going to the View menu and clicking Source.
HTTP - HyperText Transfer Protocol - The protocol responsible for delivering the contents of webpages to your computer for your viewing pleasure.
Hz - Hertz - The unit of frequency; how many times something happens per second. 1 GHz, for example, means "one gigahertz", or "one billion times per second".
IDE - Integrated Drive Electronics - An interface between the motherboard and attached storage devices (hard disk drives, optical drives).
IMAP - Internet Message Address Protocol - The protocol responsible for accessing email messages stored on a server (such as Google's or Yahoo!'s). Unlike POP3, the IMAP protocol shows you your email but retains a copy on the server.
ISO - International Organization for Standardization - Supposedly derived from the Greek word "isos", meaning "equal", and founded in 1947, they are the keepers of the communication protocol standards. Computers as we know them would not be functional without the continuous efforts of the ISO to keep things running smoothly.
LAN - Local Area Network - A group of several computers that all connect to the same central device or all share the same external connection. A router with multiple computers using it to connect to the internet is an example of a LAN. The token ring (no, not the Tolkien ring) system has all but been replaced by the ethernet system as the standard type of LAN for home and school use. If the provider of the central connection is another computer, as is often the case in a corporation, files can be stored on that computer for easy access by everyone connecting through it.
LED - Light-Emitting Diode - A semiconductor that emits light when an electric current is sent through it. The light is usually of a single wavelength, but many-wavelength LEDs exist and are used in LCD monitors. Typical applications of LEDs are indicator lights, television remote control units (which use an infrared LED), and the transmission of data through fiber optic lines. LEDs don't use much power, don't generate much heat, and tend to last a very long time, making them one of the more reliable computer parts.
LCD - Liquid Crystal Display - A type of monitor different from a CRT. Usually recognizeable by their flattened shape, they come in two flavors: active matrix and passive matrix. Though they both do the same thing, using white LEDs behind a screen of pixels, then selectively filtering the light passing through each pixel (thus obtaining the proper color) using electrical signals sent to the proper coordinates on the screen, the active matrix LCD does this in a more efficient fashion through the use of cleverly-placed transistors.
PCI - Peripheral Component Interconnect - Long, flat, white port on your motherboard. The sound card, network card, 56k modem, SCSI control card, and other add-ons are usually connected through these ports. Motherboards typically have 3-6 PCI ports, though some tiny computers are known to have only 1 PCI port.
POP3 - Post Office Protocol 3 - A protocol responsible for control over an email account. It is similar to IMAP but less advanced, as it deletes the emails from the remote server as soon as they are downloaded.
RAM - Random Access Memory - Physical sticks of memory that attach to your motherboard and store information for quick access. Their contents will be erased with a restart.
ROM - Read-Only Memory - This kind of memory doesn't get erased with a restart, because it is often powered by on onboard battery. The BIOS is stored on a such a chip.
SCSI - Small Computer System Interface - Pronounced "scuzzy". A set of instructions and protocols that allow a computer to connect to a series of either 7 or 15 devices, all daisy-chained together. It's faster than the IDE bus, but requires a controller card and also that the connected devices support SCSI.
SMTP - Simple Mail Transfer Protocol - The protocol responsible for sending email messages.
USB - Universal Serial Bus - A small, rectangular-shaped port than can support up to 127 devices daisy-chained together. Anything from mice to hard drives to printers can be hooked up through this port.
Wi-Fi - Wireless Fidelity - Another name for a wireless LAN. A wireless network allows a computer to connect to the internet or other wired network without using any wires themselves. If not properly encrypted and protected, it is possible for anyone nearby to access the network as well. The ineptitude of most people who have set up a wireless network in their houses has led to the practice of wardriving, in which people cruise around town with their laptops, trying to get free internet access or otherwise wreak havoc.
Thanks to whatis.com and How Stuff Works for information.