The term 'Towing Boat' can be abbreviated to 'TUG' which is a three letter word. A tugboat is a type of vessel that is used for towing or pushing other boats, barges, and ships. It is typically used in harbors, ports, and other shallow waters. Tugboats are usually powered by diesel engines and have a large propeller at the stern. They are also equipped with powerful winches and towlines to assist in towing operations.