In geometry, a plane is defined as a flat, infinite surface. It has infinite length and width but no thickness. A plane is thus a two-dimensional, boundless surface and a subset of space.
A plane is also defined as a set of points. Three noncollinear points, or points that don't lie on a single line, are said to lie in a unique plane. There are infinite points in a plane. A line and a point not lying on this line are also said to lie in a unique plane. In geometry, a plane is often represented as a four-sided figure on paper, which allows for the study of planes. The top of a table, the surface of a book and a page in a book are examples of portions of a plane.