Question

what is anti parallel vector​

Answer 1

vector are supported by parallel lines and are in opposite directions is called Anti parallel vector.

or

Two lines and are said to be antiparallelwith respect to the sides of an angle if they make the same angle in the opposite senses with the bisector of that angle is said as anti parallel vector

Answer 2

In a Euclidean space, two directed line segments, often called vectors in applied mathematics, are antiparallel, if they are supported by parallel lines and have opposite directions.

In that case, one of the associated Euclidean vectors is the product of the other by a negative number.