Have a birthday is an expression used to celebrate someone's special day. It is usually said to someone who is having their birthday, and it is a way of wishing them a happy birthday. The term 'have a birthday' can also be used to describe the act of celebrating one's own birthday. The crossword solution for this term is AGE, which is a three-letter word that refers to the amount of time someone has been alive. AGE is typically measured in years, and it is used to determine how old someone is.