Special Relativity:A theory developed by Albert Einstein that describes the relationship between space and time for objects moving at constant velocities, with the key principles of the constancy of the speed of light and the relativity of simultaneity.
General Relativity:A theory developed by Albert Einstein that describes the relationship between space, time, and gravity, with the key principle that gravity is a consequence of the curvature of spacetime caused by the presence of mass and energy.
Frames of Reference: The coordinate systems used to describe the motion and position of objects, which can be either inertial (non-accelerating) or non-inertial (accelerating).