Introduction to Geometry: Parallel and Perpendicular Lines

Parallel Lines and Transversals

If a line intersects a set of parallel lines it is called a transversal.

In the figure below, line RS intersects parallel lines AB and CD at points E and F. Therefore, line RS is a transversal with respect to line AB and line CD.

parallel lines AB and CD, cut by transversal RS.  Segment RS intersects segment AB at point E and segment CD at point F