A bar bill or bar tab is an account of debt owed to a bar by a patron for goods and services.
While under the impression that Julian Bashir and Miles O'Brien were dead, Quark gave a toast in their honor, "They were good customers. They always paid their bar bills on time." Quark's could think of no greater tribute. (DS9: "Armageddon Game")
After being informed of Morn's apparent destitution at the time of his death, Quark commented that Morn had always paid his bar bills on time and that money had to have come from somewhere. (DS9: "Who Mourns for Morn?")
Worf disputed responsibility for a bar bill with Quark, but eventually paid it after Quark menioned that it would not be good if word got out that he was refusing to honor the debts incurred by his own House. (DS9: "Prodigal Daughter")