BYOB is an acronym with several similar yet related expansions. The acronym is most often associated with a social gathering (a party) at which the host will not be providing alcoholic beverages; the guests are invited to bring a beverage of their choice for their own consumption.
Common expansions of the acronym include:
Bring Your Own Bottle
Bring Your Own Booze
Bring Your Own Beer
Bring Your Own Beverage