Rat out is a slang term that refers to revealing information about someone to authorities, colleagues, or anyone else for personal gain or as a form of revenge. There are several synonyms for rat out, including snitch, betray, tattle, blab, squeal, inform, and collaborate. Each of these terms has varying degrees of negative connotations, with snitch and betrayer being the harshest. On the other hand, inform or collaborate may refer to voluntarily sharing information to help someone or in the interest of truth. Regardless, anyone who rats out another is generally viewed unfavorably in social circles and can be detrimental to their own reputation.