costume party
noun [ C ] US uk/ˈkɒs.tʃuːm ˌpɑːr.ti/ us/ˈkɑː.stuːm ˌpɑːr.t̬i/
化妆舞会，假面舞会
a party where people wear special clothes that make them look like a particular character, animal or object
She went to a costume party dressed as a pirate. 她打扮成海盗去参加化妆舞会。