An arc is a continuos piece of a circle. An arc is a portion of a circle.
In the given figure, A and B are two points on the circle. The portion of circle between A and B is the arc of the circle.
SAS congruency criterion:
Two triangles are said to be congruent, if two sides and the included angle of a triangle are equal to the corresponding sides and the included angle of the other triangle.
ASA congruency criterion:
Two triangles are said to be congruent, if two angles and their included side of one triangle are equal to the corresponding angles and the included side of the other triangle.
SSS congruency criterion:
If three sides of a triangle are equal to the three corresponding sides of another triangle, then the triangles are congruent.
For example, consider the following triangles ABC and PQR. You can verify by measuring the sides of these triangles that AB = PQ, BC = QR and AC = PR. Thus, by using SSS congruence criterion you can say that these triangles are congruent.
RHS congruency criterion: