Parallels and Perpenducilars

Parallel - two lines (rays, segments) are parallel if they are COPLANAR and EQUIDISTANT throughout their length.

Coplanar - A set of points is said to be coplanar if and only if they lie on the same geometric plane.
Equidistant - Equally distant. For example, any two points on a circle are equidistant from the center.

Perpendicular - two lines (rays, segments) are perpendicular if they are COPLANAR and Intersect at a 90 "degree" angle.