Bernoulli's Principle describes the relation between the pressure of a fluid and the velocity at which it is moving.
Bernoulli's principle states that as the velocity of fluid flow increases, the pressure exerted by that fluid decreases.
This principle has many applications and is used extensively in our daily life. It is this principle that makes the flight of airplanes possible. As air flows at a faster speed on the upper part of an aircraft wing than the lower, it has a lower pressure. This makes air move upwards lifting the aircraft.
It can also be seen when a fluid moves continuously through a pipe. Where the pipe constricts, the speed of flow increases and there is a corresponding decrease in the pressure.