A boat, like a ship, is a vehicle designed for the purpose of ship transport, i.e. effecting passage or transportation across water. It is usually smaller than a ship, and in fact sometimes carried by a ship.
see Norfolk wherry, Dutch Barge, Luxemotor, Tjalk, Peniche, Yachting, Cruising, Sailboat, Lifeboat, Dinghy, Canoe, Kayak, Folding boat, Motorboat, Powerboat Jetboat, Rigid Hulled Inflatable Boat (RIB), Whaleboat, Pinnace, Raft, Ferry, Dhow, Go-fast boat, Felucca.
In rowing, a boat refers to the collection of people rowing a particular shell, which is the term applied to the actual vehicle. So a university might refer to its first boat, meaning the rowers who make up their best team, rather than their best piece of equipment.