Proof mark is a term used in the publishing industry to refer to symbols that are used to indicate changes or corrections to a document. The three most common proof marks are caret (5 letters), STET (4 letters) and DELE (4 letters). Caret is used to indicate that something should be inserted at that point, STET is used to indicate that no change should be made, and DELE is used to indicate that something should be deleted.