Projective plane

Summary

A projective plane is an incidence structure in which two points lie on exactly one line and two lines meet in exactly one point. It is the plane of perspective drawing, where parallel lines meet at a point at infinity. The real projective plane and the planes $\mathbb{P}^2(k)$ over fields are examples, and there are also planes that come from no field. Finite projective planes are central objects of combinatorics.