Definition:Congruence (Geometry)

Definition
In the field of Euclidean geometry, two geometric figures are congruent if they are, informally speaking, both "the same size and shape". That is, one shape can be overlaid on the other with a series of rotations, translations, and reflections.

Specifically, all corresponding angles of the congruent shapes must have the same measurement, and all corresponding sides of the congruent shapes must be be the same length.

Also see

 * Triangle Side-Angle-Side Equality
 * Triangle Side-Side-Side Equality
 * Triangle Angle-Angle-Side Equality