Cauchy's Theorem is a fundamental result in group theory, a branch of mathematics that studies algebraic structures known as groups. The theorem states that if a group has a finite order and a prime number divides the order of that group, then the group contains a subgroup whose order is equal to that prime number. This is significant because it helps in understanding the structure of groups and their subgroups. The theorem is named after the French mathematician Augustin-Louis Cauchy, who made important contributions to various fields of mathematics. Cauchy's Theorem is often used in the study of finite groups and plays a crucial role in the classification of groups, aiding mathematicians in their exploration of group properties and behaviors.