Congruent triangles are triangles that are identical in shape and size. This means that all corresponding sides and angles of the triangles are equal. If you were to place one triangle on top of the other, they would perfectly overlap without any gaps or mismatches. There are several ways to prove that two triangles are congruent, including the Side-Side-Side (SSS) criterion, where all three sides of one triangle are equal to the three sides of another. Other methods include Angle-Side-Angle (ASA) and Side-Angle-Side (SAS). These criteria help in establishing the congruence of triangles in geometry.