ボトルキープ

Etymology
, from the practice of the bartender keeping the bottle at the bar.

Noun

 * 1) the practice of buying a full bottle of liquor or other alcoholic beverage at a bar and having the bartender keep the unfinished bottle until the purchaser's next visit

Verb

 * 1) to keep one's own bottle of liquor or other alcoholic beverage at a bar

Usage notes
Also encountered as a noun followed by :