>>2536986A projection system is basically slang.
You can map all the points on the oblate spheroid representing earth and that's called a Geographic Coordinate System (WGS/NAD).
You can translate the Oblate Sphere into a flat plane and remap approximate grids and that's a Projected Coordinate System (Albers, Wattermen.
The combination of these is what people generally call a map projection.
So, for example, you take a WGS-84 mapped oblate sphereoid wrap it in a cylinder and use the Mercator conversion and now you have a flat map.
Look into EPSG code 4326 if you want to follow the rabbit hole.
