If the hypotenuse and a leg of one right triangle are congruent to the hypotenuse and a leg of another right triangle, then the triangles are congruent.
In simpler terms: If you have two right-angled triangles, and you know that their hypotenuses (the longest side) are the same length, and one pair of legs (the shorter sides) are the same length, then the triangles are identical in shape and size.