noun

• (uncountable) The state of being relative to something else; the absence of universally applicable rules or standards; relativism; (countable) an instance of this.
• (specifically) Also Einsteinian relativity: the reliance of the nature of physical phenomena (such as gravity, light, mass, and time) on the relative motion between an observer and the thing observed, as developed by Albert Einstein in two theories, special relativity and general relativity.
• (countable, chiefly in the plural) An evaluation of the similarities and differences between things; a comparison; hence, a difference in position or status between things; a disparity.
• (economics, specifically) The difference in pay or positions between different employees in a business (internal relativity), or between different businesses (external relativity); a differential.
• (uncountable, physics) Short for principle of relativity (“the principle that the laws of physics should be the same for all observers”). [(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.]