The Full form of BRB is Be Right Back. BRB is a phrase which is usually used as a situation in chatting on social networking sites like Yahoo Messenger, Facebook, Gmail, Watsapp etc. It is used to specify a situation when a person is chatting online with someone and wants to convey to the other person that “I will return to this conversation shortly“. So, it is commonly an internet slang used by a user to show that he expects to be away from his mobile, laptop or computer for a short time.
It is also a way to show courtesy to the other user so that he does not wonder why a person is not replying anything for a while. This type of situation may come frequently in online chatting. Acronyms are very popular in online chatting these days, so the users instead of using Be Right back generally use BRB.