Sheaf of planes

In mathematics, a sheaf of planes is the set of all planes that have the same common line. It may also be known as a pencil or fan of planes.

When extending the concept of line to the line at infinity, a set of parallel planes can be seen as a sheaf of planes intersecting in a line at infinity. To distinguish it from the more common definition the adjective parallel can be added to it, resulting in the expression: parallel sheaf of planes.