A boat is a relatively small vessel for traveling through water. The basic and not always ideal difference between a boat and a ship is that a boat can be lifted aboard a ship, although there are some very large boats that can be taken aboard only large and specialized ships. Traditionally, submarines, regardless of size, are called boats.
Boats can be used for recreation or work. They can be powered by people handling paddles or oars, by sail, by various power plants, or by combinations of power sources (e.g., sail with an auxiliary diesel).
While fools will take inappropriate boats into inappropriate conditions, boats are properly equipped and designed for the worst conditions they are expected to encounter. Rescue craft, since they must venture into the conditions that sank other craft, are often the most rugged. A boat meant for holiday sailing on inland water needs far less preparation than a fishing boat that will venture into the open ocean.