BYOB is an initialism most commonly meant to stand for "bring your own bottle". BYOB may also be defined as "bring your own beer" or "bring your own booze". BYOB is often placed on an invitation to indicate that the host will not be providing alcohol and that guests are welcome to bring their own. It is also frequently used by regular bars, restaurants, or strip clubs which do not have licenses to serve liquor or alcoholic beverages in general
via en.wikipedia.org