In flat spacetime, yes. In curved spacetime there are no global frames, and you have to be a bit more careful with your definition. It would be better to say something like that they lie in a plane whose tangent vectors are everywhere spacelike.If two events are occuring in a space like hypersurface....is it that the two events will appear to be simultaneous from a frame moving with velocity ##v\lt c##
You cannot consistently describe such a thing.a frame with velocity ##v\gt c##??