A corollary is a statement that follows readily from a previously proven statement, such as a theorem. It typically derives from the conclusion of that theorem and requires minimal additional proof.
For example, if a theorem states that all angles in a triangle sum up to 180 degrees, a corollary might be that in an isosceles triangle, the base angles are equal. This corollary can be proven using the original theorem, making it a derivative result that enhances our understanding of the subject without needing an entirely separate proof.
In essence, a corollary helps to elaborate on the implications of a theorem, providing further insight and establishing relationships within mathematical concepts.