Irish whiskey was an Earth alcoholic beverage, a whiskey originating from Ireland.
Single malt Irish Whiskey was served at Miles O'Brien's birthday party in 2373. (DS9: "The Assignment")
Miles O'Brien shared an Irish whiskey with Worf after Jadzia Dax was slain by Gul Dukat in 2374. (DS9: "Tears of the Prophets").