The short term for 'Be Right Back' which usually means that people have told their friends via text or internet based social services that they have gone somewhere for a brief period of time which usually stand for the time of up to half an hour unless they've said that it would be longer. Although in some cases, the term of BRB can also mean that they have gone for more than 6 hours without any hint of what they are doing, which usually suggests that they are having a hard time trying to masturbate properly.
Dave - Hi Josh do you want to go online in a sec?
Josh - Yeah sure but brb, going to get some food.
Dave - OK :)
8 Hours Later
Josh - I'm Back
Dave - Where the hell have you been? To the other side of the planet and back?
Josh - No I went to watch about 20 movies and never mentioned it to you because I couldn't be asked telling you.
Dave - Ok :(