fancy dress

Từ điển Oxford Advanced Learner 8th

ˌfancy ˈdress [fancy dress] BrE NAmE noun uncountable (BrE)
clothes that you wear, especially at parties, to make you appear to be a different character
•guests in fancy dress
•a fancy-dress party
see also ↑costume, ↑masquerade

Example Bank:
•Many of the marathon runners compete in fancy dress.
•Several of the managers donned fancy dress for the office party.
•I went to a fancy dress party as a pirate.
•The streets were full of people in fancy dress.