is: a three-dimensional physical setting, such as a laboratory, which provides the assumed context in which events takes place. [P2.7]
is normally: fixed with respect to a specific observer. [P2.3]
is represented: by a coordinate system, that allows a unique position to be assigned to each event, and a system of suitably synchronized clocks (or some equivalent system) that enables a unique time to be assigned to each event. [P2.3]
Copyright 1997, The Open University