The Bernoulli principle states that in a flowing fluid, an increase in the fluid's speed occurs simultaneously with a decrease in pressure or potential energy. This principle is derived from the conservation of energy and applies to various fluids, including liquids and gases. It helps explain how airplanes generate lift and how fluid flows through pipes. In practical terms, the Bernoulli principle can be observed in everyday situations, such as when a garden hose nozzle is narrowed, causing the water to spray out faster. It also plays a crucial role in various engineering applications, including aerodynamics and hydraulics.