Term introduced by Herman MinkowkiMinkowski to describe the ontological status of space and time in the theory of special relativityspecial-relativity and subsequently also in general relativitygeneral-relativity and more modern theories.
As a consequenceWithin relativity (both special and general), changes of reference frames can change both the Lorentz transformations, time andnotions of space transform into eachand of time, with one depending on the other when changing reference frameas well. This calls forAs a consequence, it is necessary to treat both concepts in a unified description: Minkowskimanner. Hence the term spacetime.
The term has outgrown its original context, and is now used in other theories.