Answer:
alternate interior angles
Explanation:
∠1 and ∠4 are on opposite sides of the transversal, so are called "alternate" angles. They are both between the parallel lines, so are called "interior" angles.
∠1 and ∠4 are "alternate interior angles". Angles 2 and 3 are also alternate interior angles. The measures of alternate interior angles are the same:
m∠1 = m∠4
m∠2 = m∠3
Hence, alternate interior angles are congruent.