- Two plane figures are called congruent if one figure can be moved so that it fits exactly on top of the other figure. This movement can always be affected by a sequence of translations, rotations and reflections.
- Congruent figures have exactly the same shape and size, each part of one figure can be matched with a part of the other figure, and
- matching angles have the same size
- matching intervals have the same length
- matching regions have the same area.