# Frame of reference

In physics and astronomy, a **frame of reference** (or **reference frame**) consists of an abstract *coordinate system* whose origin, orientation, and scale are specified by a set of **reference points** ― geometric points whose position is identified both mathematically (with numerical coordinate values) and physically (signaled by conventional markers).[1]

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For *n* dimensions, *n* + 1 reference points are sufficient to fully define a reference frame. Using rectangular (Cartesian) coordinates, a reference frame may be defined with a reference point at the origin and a reference point at one unit distance along each of the *n* coordinate axes ^{[citation needed]}.

In Einsteinian relativity, reference frames are used to specify the relationship between a moving observer and the phenomenon or phenomena under observation. In this context, the phrase often becomes "**observational frame of reference**" (or "**observational reference frame**"), which implies that the observer is at rest in the frame, although not necessarily located at its origin. A relativistic reference frame includes (or implies) the coordinate time, which does not equate across different frames moving relatively to each other. The situation thus differs from Galilean relativity, where all possible coordinate times are essentially equivalent ^{[citation needed]}.