costume party
noun /ˈkɒstjuːm pɑːti/
  /ˈkɑːstuːm pɑːrti/
(especially North American English)- a party where all the guests wear special clothes, in order to look like a different person, an animal, etc.化装舞会 - They celebrated New Year's Eve with a costume party.他们举办了一个化装晚会庆祝除夕。 
 
- They celebrated New Year's Eve with a costume party.