This is geometry that is based on ordinary space-- space as we normally consider it. This is the ordinary space of 3 dimensions as you can imagine them in the coordinate system. Planes are flat, and...
In Euclidean geometry parallel lines are always the same distance apart. In non-Euclidean geometry parallel lines are not what we think of a parallel. They curve away from or toward each other. Said...
Between two points there is one straight line. A straight line may be extended to any finite length. Any circle can be described by the location of its center and the length of its radius. All right...