Vectors lying on a straight line or on parallel lines. In order that two non-zero vectors be collinear it is necessary and sufficient that their coordinates be in proportion. The zero vector is collinear with every vector. Similarly, points lying on a straight line are said to be collinear.
Collinear vectors. A.B. Ivanov (originator), Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Collinear_vectors&oldid=16118