What Is a Spatial Frame of Reference? (Cheat Sheet)
Coordinates are pairs (2D) or triples (3D) of real numbers that designate the position of a point in a coordinate system.
A coordinate system is a set of rules by which a coordinate can spatially relate a location to a unique coordinate system origin and associated axes.
A spatial reference frame ties a coordinate system's origin to some Object Reference Model, such as a model of the Earth, so that it is no longer arbitrary but tied to the real world.