A boat is a watercraft, usually smaller than most ships. Some boats are commonly carried by a ship or on land using trailers.

A boat consists of one or more buoyancy structures called hulls and some system of propulsion, such as a screw, oars, paddles, a setting pole, a sail, paddlewheels or a water jet.

Parts of a boat
 
Ancient boat in an Egyptian tomb painting from about 1450 BCEThe roughly horizontal, but cambered structures spanning the hull of the boat are referred to as the "deck". In a ship there are often several, but a boat is unlikely to have more than one. The similar but usually lighter structure which spans a raised cabin is a coarch-roof. The "floor" of a cabin is properly known as the sole but is more likely to be called the floor. (A floor is properly, a structural member which ties a frame to the keelson and keel.) The underside of a deck is the deck head. The vertical surfaces dividing the internal space are "bulkheads". Some are important parts of the vessel's structure. The front of a boat is called the bow or prow. The rear of the boat is called the stern. The right side is starboard and the left side is port.

It is somewhat risible in modern practice to call the command area of a large boat the "bridge". It is the cockpit or wheelhouse, depending on its design.

The compartments housing a toilet, and the toilet itself, are known as the "heads", and a trip to this area is a "head call".

In the old days, cordage intended for the delicate hands of a yacht's owner was of linen, later cotton. Therefore cordage used to control a sailing boat, tends to be referred to as "line" rather than rope. Most have specific names, but in general, lines used for raising things like sails and flags are "halyards" while the principal ones for adjusting the positions of the sails are called "sheets".

All the lines and wire collectively are referred to as "rigging". That which is set up in the yard and left is standing rigging. That which is adjustable in use is running rigging. For example, a forestay is standing rigging and a sheet or a halyard is part of the running rigging.