Buoyancy is the upward force acting on an object while it is as least partially submerged in a liquid. The buoyancy force can be calculated by multiplying the pressure by the area of the object. This is partially why a large, heavy object like a ship can float.
Buoyancy is also highly related to Archimedes' principle, which states that the buoyancy force is the same as the force that the displaced water, or other liquid, could exert. The volume of displaced water is also the same as the volume of the object that is submerged. If buoyancy is greater than downward forces like gravity, the object will rise or float.