A hydraulic press is referred to as a force multiplier due to its ability to amplify a small input force into a much larger output force. 

This phenomenon is primarily explained through Pascal's Principle, which states that any change in pressure applied to an enclosed fluid is transmitted undiminished to all parts of the fluid.

A hydraulic press consists of two cylinders of different diameters connected by a tube filled with oil. When force is applied to the smaller piston, it creates pressure in the fluid.

According to Pascal's Law, this pressure is transmitted equally throughout the fluid. As a result, the pressure acts on the larger piston, amplifying the applied force.

Thus, a hydraulic press is called a force multiplier.