In geometery, a transversal has several special properties when it passes through two parallel lines. Given:

 A
1|2
---->>---
3|4
5|6
---->>---
7|8
 B
In this example, the traversal is line AB, which creates angles 1-8. Here are the following special properties due to the fact that the two lines the tranversal goes through are parralel:

1 is congruent to 5, 2 is congruent to 6, 3 is congruent to 7, and 4 is congruent to 8. These are called corresponding angles.

3 and 5 are supplementary, and so are 4 and 6. This means that together, they add up to 180 degrees. These are called same side interior angles.

3 is congruent to 6 and 5 is congruent to 4. These are called alternate interior angles.
There are also several vertical angles that would be congruent, but I don't mention it because it's not a direct result of a transversal going through two parralel lines