BYOB or BYO is an initialism meant to stand for "bring your own bottle", "bring your own beer", "bring your own beverage", 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. Some business establishments allow patrons to bring their own bottle, sometimes subject to fees or membership conditions, or because the establishment itself does not have license to sell alcohol.
The term is cited by some online sources to have been used first in the early 1970s to mean "bring your own bottle (of wine)", although in present-day it is just as likely to mean "bring your own booze" or "bring your own beer". It was used by small restaurants that did not have liquor licenses, but which were responding to the new popularity of wine among Americans by advising customers that they could BYOB and drink it with their meal.
Some establishments that sell alcoholic beverages for on-site consumption, such as bars or restaurants, may also allow patrons to bring their own alcohol purchased from elsewhere. That alcohol is usually subject to an opening fee. Often the rule is limited to bottles of wine, where the fee is known as corkage or a corking fee. Such policies are greatly regulated by local liquor control laws and licensing restrictions.
As an alternative to the traditional full-service liquor license, some jurisdictions offer a similar license known as a bottle club license. It allows the business establishment to serve alcohol on the premises, but only if patrons brought the alcohol from elsewhere. The license generally prohibits the business from selling its own stock of alcoholic beverages. The license may require that patrons be members of the establishment. Such licenses may be preferred in situations where fees or zoning conditions imposed by a full-service liquor license are unwanted or impractical. They may also be the only license available, as some jurisdictions impose full-service liquor license quotas or business class restrictions.
In Australia and New Zealand, the term "BYO" (Bring Your Own) emerged to describe business establishments that offered corkage. It is believed that restaurants in Melbourne, in the state of Victoria, were advertising as "BYO" establishments by the 1960s with the concept becoming popular in New Zealand in the late 1970s.
Legally, using New Zealand as an example, if your premises only holds an on-licence-endorsed (BYOB license), you as an owner and duty manager with a General Manager's Certificate are forbidden to have a wine list and sell alcohol on the premises. You must have both On-License & On-License-Endorsed to have a wine list and allow BYOB, thus calling your restaurant 'fully licensed'