coordinate system
From Glossary of Meteorology
(Also called reference frame.) Any scheme for the unique identification of each point of a given continuum.
These may be points in space (Eulerian coordinates) or parcels of a moving fluid (Lagrangian coordinates). Newton's laws of motion do take different forms in different systems (
see inertial coordinate system, relative coordinate system). The geometry of the system is a matter of convenience determined by the boundaries of the continuum or by other considerations (
see Cartesian coordinates, curvilinear coordinates).