[Geekcop]

A lot of this has been addressed in assorted threads on this site already, so using the search function should be your first move. That being said, here's a brief glossary of some terms you'll see around here.

ROM-Read Only Memory; this is the brain of your device
Cook-This term is used to describe the creation of a customized ROM
Kitchen-The software used to create a custom ROM
Flashing-The act of putting your new custom ROM onto your device
Bricking-Device failure, usually permanent; what can happen if a ROM is improperly cooked or flashed
.Cab-Means of packaging an app for use on a device. Cabs can be d/l'd directly to your device and then run. Apps packaged in the .exe format need to be d/l'd to your PC, then transferred to your device by means of a sync cable
Modding-Modifying your device by adding 3rd party apps and/or custom ROMs

That's my $.02..Others will have much more to add