Definition:Transversal (Geometry)

Definition
A transversal of two lines lying in the same plane is a line which intersects them in two different points.

The transversal is said to cut the two lines that it crosses.


 * Alternate Interior Angles.png

Interior Angles
Interior Angles are the angles which are between the two lines cut by a transversal.

In the above figure,$\angle AEF$, $\angle CFE$, $\angle BEF$, and $\angle DFE$ are interior angles.

Alternate Interior Angles
Alternate interior angles are the angles which are between two lines cut by a transversal, on opposite sides and different lines.

In the above figure, $\angle AEF$ and $\angle DFE$ are a pair of alternate interior angles, as are $\angle CFE$ and $\angle BEF$.

Corresponding Angles
Corresponding Angles are the angles in equivalent positions on the two lines cut by the transversal with respect to the transversal.

For example, $\angle AEF$ and the angle from $C$ to $F$ and then down along $EF$ are corresponding angles.

Also see

 * Equal Alternate Interior Angles implies Parallel Linesl
 * Equal Corresponding Angles or Supplementary Interior Angles Implies Parallel
 * Parallel Implies Equal Alternate Interior Angles, Corresponding Angles, and Supplementary Interior Angles