An origin is
a starting point. It is the zero mark on a number line, or the point
where coordinate axes cross.

In Geometry, the origin of a Euclidean
space is a special point, usually denoted by the letter O, used
as a fixed point of reference for the geometry of the surrounding
space.

In two dimensions it is the point with coordinates (0,0)
and in three dimensions it is the point with coordinates (0,0,0).