Definition of: relativity

(rel′ə·tiv′ə·tē) noun
1. The quality or condition of being relative; relativeness.
2. Philos. Existence only as an object of, or in relation to, a thinking mind; phenomenality: sometimes called the doctrine of the relativity of existence.
3. A condition of dependence or of close relation, as of the solar system on the sun.
4. Physics The principle of the interdependence of matter, energy, space, and time, as mathematically formulated by A. Einstein. The special theory of relativity states that the velocity of light is independent of the motion of its source and that motion itself is a meaningless concept except as between two physical systems or material bodies moving relatively to each other. The general theory of relativity extends these principles to the law of gravitation and the motions of the heavenly bodies.