asa means Angle Side Angle and it is used to prove the congruence of triangles, meaning if an angle, side and angle of two triangles are equal, then the triangles are congruent
(Angle-Side-Angle) Two angles and the included side of a triangle are congruent to the corresponding parts of another triangle, then the triangles are congruent. Just type in ASA of a triangle on google images and you will find perfect examples (:
