In geometry, two figures or objects \displaystyle{ F } and \displaystyle{ F' } are congruent (written as \displaystyle{ F \cong F' }) if they have the same shape and size, or if one has the same shape and size as the mirror image of the other.
More formally, two sets of points are called congruent, if and only if one can be transformed into the other by isometry. For isometry, rigid motions are used.