Definition of

Alternate Interior Angles

When two lines are crossed by another line (the Transversal), a pair of angles
• on the inner side of each of those two lines
• but on opposite sides of the transversal
are called Alternate Interior Angles.

c and f are Alternate Interior Angles.
d and e are Alternate Interior Angles.

So there are actually two pairs!

Play with it below (try dragging the points):