Galilean Relativity is a principle in physics that states the laws of motion are the same in all inertial frames of reference. This means that if you are moving at a constant speed in a straight line, the laws governing your motion will appear the same to you as they do to someone at rest. This concept was formulated by Galileo Galilei in the early 17th century. In practical terms, if two observers are moving relative to each other at constant velocities, they will each measure the same physical phenomena, such as speed and acceleration, but may disagree on the absolute position or time. This principle laid the groundwork for later developments in physics, including Isaac Newton's laws of motion.