A reveller is someone in the middle of noisy fun — singing, dancing, drinking, filling the streets at a festival or on New Year’s Eve. News writing uses it a lot: “revellers poured into the square.” It can sound warm, or it can hint that the crowd is too loud or too drunk; the tone depends on the writer. The British spelling is reveller (revel + -er, with a double l); American spelling is usually reveler. It names the person, not the party itself.