Meaning of “dress up” - Learner’s Dictionary

dress up

phrasal verb with dress us uk /dres/ verb

to put on formal clothes for a special occasion:

Weddings are a great opportunity to dress up.

to wear special clothes in order to change your appearance, usually for a game or party:

He dressed up as Superman for the party.

(Definition of “dress up” from the Cambridge Learner’s Dictionary © Cambridge University Press)