Meaning

noun (physics) the theory that space and time are relative concepts rather than absolute concepts

noun the quality of being relative and having significance only in relation to something else

originFrom relative (“connected to or depending on something else”) + -ity (suffix forming nouns from adjectives where the nouns refer to the properties, qualities, or states described by the adjectives). Sense 2.1 (“reliance of the nature of physical phenomena on the relative motion between an observer and the thing observed”) is a translation of German Relativität (“relativity”) used in the works of…

Etymology from Wiktionary, CC BY-SA 3.0