(CoordinateX,CoordinateY)
The used unit depends on the context. Be especially careful when looking at the CoordinateY, which sometimes does not use the same unit as the CoordinateX, for example planelines instead of pixels. Areas are written like this:
(StartCoordinateX,StartCoordinateY) - (EndCoordinateX,EndCoordinateY)
Regarding the used unit the same things apply.