Congruence
This means that two geometrical figures are congruent if one object can be repositioned, rotated or reflected—but not resized—so that it coincides exactly with the other object. if one can be moved or rotated so that it fits exactly where the other one is, then the two figures are congruent. If one of the object has to change its size, then the two objects are not congruent: they are just called similar.