Pascal's law states that when pressure is applied to a confined fluid, the pressure change is transmitted equally in all directions throughout the fluid. This principle is fundamental in understanding how hydraulic systems work, such as in hydraulic brakes and elevators. The law is named after the French mathematician and physicist Blaise Pascal, who formulated it in the 17th century. It highlights that the pressure exerted on a fluid at rest is uniform, which allows for the efficient transfer of force in various applications, making it essential in engineering and physics.