The general theory of relativity (or general relativity for short) is a major building block of modern physics. It explains gravity based on the way space can 'curve', or, to put it more accurately, it associates the force of gravity with the changing geometry of space-time.

General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime.

General relativity is Einstein's theory of gravity, in which gravitational forces are presented as a consequence of the curvature of spacetime. In general relativity, objects moving under gravitational attraction are merely flowing along the "paths of least resistance" in a curved, non-Euclidean space.

General relativity explains the law of gravitation and its relation to the forces of nature. It applies to the cosmological and astrophysical realm, including astronomy. The theory transformed theoretical physics and astronomy during the 20th century, superseding a 200-year-old theory of mechanics created primarily by Isaac Newton.