A [[../Math/Coordinate System|Coordinate System]] used in 3D graphics (typically when using [[Perspective Projection]]) where any [[../Math/Vector|Vector]] in $\R^4$ is thought to be [[../Math/Homogeneous Equivalence|Homogeneously Equivalent]] to a [[../Math/Point|Point]] in $\R^3$ after performing a [[Perspective Divide]]. $\huge \mat{ x\\y\\z\\w } \equiv \frac{1}{w} \mat{ x\\y\\z } $ If $w > 0$