Used in casual conversations, not in formal situations or writing. At the reunion, Clara was the chatterbox, lively discussing every little event.
Pro Tip 2/3
Often Affectionate
Usually said in a friendly or teasing way about someone close to you. My nephew is a little chatterbox, always sharing his adventures.
Pro Tip 3/3
Personal Interest
Implies the speaker may talk about things mostly interesting to themselves. As soon as he starts talking about trains, the chatterbox in him comes out.