A cocktail was a type of beverage, usually containing several types of alcohol mixed together. Examples of cocktails were gin and tonic, martini, mint julep, Moscow Mule and vodka martini. Cocktails could be served at a cocktail party and were sometimes served by a cocktail waitress.
When the Evora delegation started eating the flowers on the tables before a reception onboard the USS Enterprise-E in 2375, Beverly Crusher joked that apparently the Evora didn't believe in cocktails before dinner. (Star Trek: Insurrection)
In 2374, Quark complained about the fire-suppression system in his bar. According to him every time he served a flaming cocktail, the system engaged and snuffed out the fire. (DS9: "Honor Among Thieves")