"For over two thousand years, the adjective 'Euclidean' was unnecessary because no other sort of geometry had been conceived. Euclid's axioms seemed so intuitively obvious that any theorem proved from them was deemed true in an absolute sense. Many other consistent formal geometries are now known, the first ones being discovered in the early 19th century. It also is no longer taken for granted that Euclidean geometry describes physical space. An implication of Einstein's theory of general relativity is that Euclidean geometry is only a good approximation to the properties of physical space if the gravitational field is not too strong."
Euclidean geometry - Wikipedia, the free encyclopedia
