Key

A key is a unique identifier in Second Life (often referred to as a UUID) for anything mostly, be it a prim, avatar, texture, etc.

The key itself is formed of alphanumeric characters (a-z and 0-9) and each section of the key is broken up by dashes.

An example key:

a822ff2b-ff02-461d-b45d-dcd10a2de0c2