The "Side-Angle-Side (SAS)" theorem is a fundamental principle in geometry that helps determine the congruence of triangles. According to this theorem, if two sides of one triangle are equal in length to two sides of another triangle, and the angle between those two sides is also equal, then the two triangles are congruent. This means they have the same shape and size. In practical terms, SAS can be used in various applications, such as in construction and design, where ensuring the accuracy of triangular shapes is crucial. Understanding SAS is essential for students studying geometry and is often one of the first congruence criteria taught in mathematics classes.