PQ and RS are two parallel lines. A third line 'm' intersects them at X and Y.
Hence 'm' is transversal to the two parallel lines. Refer figure at the top.
Angles Formed by Transversal
In the adjacent animation, two parallel lines PQ and RS are cut by a transversal 'm'. Then, the following eight angles are formed:
∠1, ∠2, ∠3, ∠4, ∠5, ∠6, ∠7 and ∠8.
Interior angles: When two parallel lines are cut by a transversal, then the angles formed inside the lines are called interior angles. Of the eight angles above, ∠3, ∠4, ∠5 and ∠6 are interior angles.
Exterior angles: When two parallel lines are cut by a transversal, then the angles formed outside the lines are called exterior angles. Out of the eight angles formed, ∠1, ∠2, ∠7 and ∠8 are exterior angles.
A transversal that cuts two parallel lines at right angles is called a perpendicular transversal. In such case, all 8 angles are right angles.