What does fessing up mean?

"Fessing up" means to admit to something you've done wrong or something you've been hiding. It's a more informal and colloquial way of saying "confess" or "admit."

Here are some examples:

* "He finally fessed up to stealing the money."

* "I'm going to fess up to eating all the cookies."

* "She fessed up to her part in the prank."

The word "fess" is a shortened form of "confess," and "up" emphasizes the act of revealing something.