Best definition
When slutty college girls dress up as even bigger sluts on Halloween night. Whoreaween costumes include skirts that cut above

mid-thigh, shirts that show maximum cleavage, and platform shoes/high heels. These girls usual travel in packs of three or more.

You girls ready for Whoreaween? I hope you’re wearing your fishnet stockings.
Whoreaween: define #2
When members of the female gender use the festivities of Halloween as an excuse to dress up like prostitutes, regardless of how attractive said members are.
Even the fuglies at my job dress up for Whore-aween.