The abbreviation "brb" stands for "be right back." It is commonly used in digital communication, like texting or chatting online, to inform the other person that you will temporarily leave the conversation but will come back shortly. It's a way to let others know that you are not ignoring them, but rather stepping away for a moment.
"Brb" originated from early internet chat and messaging systems in the late 1990s and early 2000s. It is an example of "text speak," which simplifies language for quicker communication, especially in informal contexts.