I’m compiling a glossary of only the most common terms on this page. For a far more comprehensive glossary, take a look at the excellent SL lexicon at San José State University’s School of Library & Information Science:
or Stella Costello’s ‘Second Life Vocabulary’ at:
Avatar: generic term for a 3D graphical representation of the self in any inhabited virtual environment. You can customise the appearance of your avatar by right-clicking and selected Appearance from the pie menu.
Linden Dollar: the in-world currency of SL, exchangeable for real dollars (or, through third-party traders, euros, sterling, and a host of other currencies.)
Pose ball: a small positionable coloured ball with which a pose (such as sitting) or animation (such as dancing) is associated. Generally activated by right-clicking and selecting ‘Sit here’ from the pie menu.
Prim: short for ‘primitive’, the 3D geometric solids that are the basic building blocks of SL.
Rez (or rezz): to create and object, or to make an object appear, in-world. Most commonly used in two contexts:  when logging in or when teleporting to a new location, the scene may be “slow to rez”, i.e. to resolve;  to ‘rez’ an object in your inventory by dragging it into the world.
Sim: abbreviation for ‘simulator’, common name for a region in SL.
UUID: Universally Unique Identifier. Every digital resource (avatar, object, texture, event, group, land parcel, transaction, snapshot … everything!) is identified by its unique (16-byte) reference. You’ll probably not need to know this, but it’s useful to know it (for example, for configuring the tourHUD that you’ll be using as Kingston University ‘noobies’; and, more generally, for scripting objects, where you may need to reference textures, sounds, etc).
Short forms in text communication (chat, IM)
Common text short-cuts, many in common with SMS messaging and other IM chat. I’d generally discourage ‘SMSese’, but the following are both useful short-cuts and commonly understood:
afk: “away from keyboard”
brb: “be right back”
IM: “instant message”. As in “IM me if you want to talk”
tp: “teleport” (from one location to another). As in “shall I tp you to my location?”
ty: “thank you”