What does cocktail attire refer to?

Its basically Since the name for this style can be misconstrued and confused with casual wear, it is often called business attire or western business. The most common way in which a man can dress in informal attire is by wearing a two-piece suit.

Similarly, women may wear a light or dark colored dress, suit, or dressy separates, though this would be verging on "business attire," which is slightly more casual; the nature of the event and the list of people attending may further help in deciding.