open bar

noun
  1. a bar at a reception that serves drinks whose cost has been borne by the host, an admission charge, a sponsor, etc.: Before the banquet there will be an open bar from 5 to 7 p.m.
Compare cash bar.

Origin of open bar

First recorded in 1970–75
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018