BRB

Stands For
Be Right Back

Which means
BRB is used in chatspeak to say that you will not be available to chat for the following period of time, usually until you say "Back" or something of that sort.

Example
Moe: I have to go do something... BRB.

Joe: Ok.

(4 minutes later)

Moe: I'm back!

Related Acronyms

 * None.