Collinear vectors are those vectors that act either along the same line or along parallel lines. These vectors may act either in the same direction or in opposite directions.
angle between them is 00, as shown in the figure below. When vectors act along the same direction, they are called parallel vectors.
If two collinear vectors act in opposite directions, then the angle between them is 180o or p radians, as shown in the figure below.
Vectors are said to be anti-parallel if they act in opposite directions.
