plural of REL

Initialism of Russo-European Laika.

(relativity) A theory that (neglecting the effects of gravity) reconciles the principle of relativity with the observation that the speed of light is constant in all frames of reference.

(relativity) A theory extending special relativity and uniformly accounting for gravity and accelerated frames of reference, postulating that space-time curves in the presence of mass.

(relativity) The principle that only the motion of objects relative to one another can be measured, and that there is no absolute frame of reference.

(physics) The theories of special relativity and general relativity, two theories in physics developed mainly by Albert Einstein at the beginning of the 20th century from which several important results such as the equivalence of matter and energy and the Einstein field equations are derived.

plural of theory of relativity

Synonym of relativity (either Albert Einstein's special relativity or general relativity)

(grammar) A pronoun that introduces a relative clause and refers to an antecedent. Some words that can be used as interrogative pronouns can alternatively be used as relative pronouns: what, which, who, and whom. The other relative pronouns are whoever, whomever, whatever, and that.

(grammar) A relative pronoun used in an adjectival clause.