Alternate Interior Angles forms when two parallel lines cut by transversal.
Explanation:
Transversal is a line that intersects two or more lines.
Alternate Interior Angles forms when two lines are cut by a Transversal, the pairs of angles on either side of the transversal and inside the two lines.
Take 8 angles, 1,2,3,4,5,6,7 & 8 present on the lines A & B. Let C is a transversal cutting the lines A & B.
Here the pairs of angles are 1 & 5, 2 & 6, 3 & 7, 4 & 8.
Alternate Interior angles are 3 & 5, 4 & 6.
If two parallel lines are cut by a transversal, then the alternate interior angles should form congruent.