 Manifold of Events. Consider our universe, which relativistic cosmologies attempt to model. Its spacetime is the entirety of all space through all time. The events of this spacetime are generalizations of the dimensionless points of ordinary spatial geometry.  A geometric point in ordinary spatial geometry is just a particular spot in the space and has no extension.  Correspondingly, an event in spacetime is a particular point in a cosmological space at a particular moment of time.