From Longman Dictionary of Contemporary Englishopen barˌopen ˈbar noun [countable] American English DFDDRINKa bar at an occasion such as a wedding, where drinks are served free
Examples from the Corpus
open bar• At the moment we use a combination of electric oil heaters and open bar fires.• Employees stayed late every night to drink from the open bar and banter about advertising concepts with their mentor.• I can see him through the open bar. 