Coordinates are used to describe locations. Each one is a group of "ordinate" numbers which taken together can be plotted on a grid, one ordinate per dimension.
Coordinates in Source are
(X,Y,Z), where X is forward/East, Y is left/North, and Z is up.
(0,0,1) is a point one unit directly above the origin.
Coordinates are often stored alongside a set of rotation angles.
The origin of an object is the point at which its local coordinates are
(0,0,0). It is the mathematical centre from which local coordinates are relative. It is rarely the centre of the visible object, however.