Proof notation is a type of notation used in proofreading and editing. It is a system of symbols and abbreviations that are used to indicate corrections, queries, and other editorial comments. The most common proof notation is STET, which stands for 'let it stand'. This notation is used to indicate that no changes should be made to the text. STET is often used when an editor or proofreader has changed their mind about a suggested correction or query.