A boat is a watercraft of any size designed to float or plane, to work or travel on water. Small boats are typically found on inland (lakes) or in protected coastal areas. However, boats such as the whaleboat were designed for operation from a ship in an offshore environment. In naval terms, a boat is a vessel small enough to be carried aboard another vessel (a ship). Another less restrictive definition is a vessel that can be lifted out of the water. Some definitions do not make a distinction in size, as bulk freighters long on the Great Lakes are called oreboats. For reasons of naval tradition, submarines are usually referred to as 'boats' rather than 'ships', regardless of their size and shape.

A boat is a nautical craft of modest size.