Geometric Question:

angles on the opposite sides of the transversal and on the interior of the parallel lines
The pair of angles in between the two lines cut by the transversal and on alternate sides of the transversal. Alternate interior angles are congruent if and only if the two lines crossed by the transversal are parallel.
Two angles that are on the inside of the parallel lines and opposite sides of the transversal. These types of angles are always congruent to one another.
The pair of angles in between the two lines cut by the transversal and on alternate sides of the transversal. Alternate interior angles are congruent if and only if the two lines crossed by the transversal are parallel.
The stylish pair of angles that are in between the two lines cut by the transversal and on alternate sides of the transversal. They're congruent if and only if the two lines crossed by the transversal are parallel.