The term 'scull propeller' refers to a type of propulsion system that uses an OAR (3 letters) to move a boat through the water. This type of propulsion system is often used in small boats, such as canoes and kayaks, as it is relatively easy to use and requires minimal effort from the user. The OAR is held in one hand and is used to push against the water, creating a propelling force that moves the boat forward.