Segment
Part of a line consisting of two endpoints and all points between them.
Ray
Part of a line consisting of one endpoint and all the points of the line on one side of the endpoint.
Opposite Rays
Two collinear rays with the same endpoint.
Parallel Lines
Coplanar lines that do not intersect.
Skew Lines
They are noncoplanar; they are not parallel and do not intersect.
Parallel Planes
Planes that do not intersect.