Given distinct points "A" and "B", they determine a unique ray with initial point "A". As two points define a unique line, this ray consists of all the points between "A" and "B" (including "A" and "B") and all the points "C" on the line through "A" and "B" such that "B" is between "A" and "C". This is, at times, also expressed as the set of all points "C" such that "A" is not between "B" and "C". A point "D", on the line determined by "A" and "B" but not in the ray with initial point "A" determined by "B", will determine another ray with initial point "A". With respect to the "AB" ray, the "AD" ray is called the "opposite ray".