What does the term 'Proof-based Geometry' mean?

Euclid developed his sytem of Geometry in a rigorous, logical manner. Each idea was only accepted as true if it could be proved to be true based on ideas that were already known and accepted. A formal proof is the logical demonstration that a particular theorem is true. The Geometry course described here uses proofs and logical reasoning in this manner to develop much of the material that is covered during the class.  more