BRB is an internet slang initialism used online when a person needs to leave a conversation momentarily. It stands for "be right back" and is usually used in chats and on an instant messenger service. It is often used as a way to express politeness, so that other users do not wonder why a person is not saying anything for a while. BRB is commonly used in emails, messages sent using an instant messaging service, etc. when you have to leave your computer, etc. for a short time.