What are corresponding parts?

Corresponding parts can be described using many different examples. I'll use right triangles. By definition, one of the interior angles of a right triangle is 90o. Therefore the other two interior angles of a right triangle must add up to 90o since the sum of all three interior angles of a triangle is equal to 180o. In fact, the two corresponding angles of any other right triangle must add up to 90o. Those angles are corresponding parts of a right triangle. The 90o angle is another, albeit different, corresponding part of a right triangle.

This can be generalized to pretty much anything you're talking about as long as what your talking about has parts. Take a person's face for example. I have blue eyes. You may have green eyes. Green would be the color of your corresponding facial feature to my blue.