Alternate Exterior Angles
When two lines are crossed by another line (called the Transversal):
The pairs of angles on opposite sides of the transversal but outside the two lines are called Alternate Exterior Angles.
In the example, these are Alternate Exterior Angles:

To help you remember: the angle pairs are on Alternate sides of the Transversal, and they are on the Exterior of the two crossed lines.
Parallel Lines
When the two lines being crossed are Parallel Lines the Alternate Exterior Angles are equal.
(Click on "Alternate Exterior Angles" to have them highlighted for you.)