(physics) An n-dimensional continuum consisting of dimensions of both space & time. Normally spacetime is considered as having 4 dimensions (x, y, z, t), but higher-dimensional spacetimes are often encountered in theoreticalphysics, e.g. the 5-dimensional spacetime of Kaluza-Klein theory or the 11 dimensions of spacetime in M-theory.
(relativity) A specific region of the universe with mathematically different properties than the surrounding spacetime. Synonymous with "metric" within the context of general relativity."a Schwarzschild spacetime," "a Reissner-Nordström spacetime," etc. as opposed to sense (2) describing the universe's spacetime as a whole: "a Minkowski spacetime," "a 5-dimensional spacetime," etc.
