homogenous coordinates
A set of n+1 coordinates used to represent points in n-dimensional projective space. Points in projective space can be thought of as points in Euclidean space together with some points at infinity. The coordinates are homogenous because a scaling of each of the coordinates by the same nonzero constant doesn't alter the point to which the coordinates refer. Homogeneous coordinates are useful in the calculations of projective geometry, and thus in computer graphics, where scenes must be projected onto a window.