congruence

Two figures are congruent if one can be transformed into the other by an isometry, i.e. a combination of rigid motions, explicitly a translation, a rotation, and/or a reflection.

Two figures are congruent if they are the same shape and size.

Two line segments are congruent if they have the same length.
Two angles are congruent if they have the same measure.
Two circles are congruent if they have the same diameter.

See also: similarity