A mizzen (or mizen) is the aftmost (rear) mast or sail on a sailing vessel with three or more masts, or the shorter, aft mast on a two-masted vessel like a ketch or yawl. It is primarily used to assist with steering, balancing the boat (acting as a "rudder"), and reducing yawing (swinging) while at anchor.

Key Details:
Location: Always positioned behind the mainmast, typically near the stern.

Function: Enhances maneuverability and helps control the balance of the boat, particularly by keeping the bow pointed into the wind.

Types: On a ketch, the mizzen mast is located forward of the rudderstock, whereas on a yawl, it is located aft of the rudderstock.

Etymology: Derived from the Old French mizaine or Italian mezzana, potentially relating to "middle" (medianus) or a "moderate" size.

On three-masted ships, the mizzen is the third mast from the bow. It is often used for setting a "steadying sail" to provide stability in high winds or while anchored.