Zero or Null Vector

A vector whose initial and terminal points are coincident is called a zero or null or a void vector. The zero vector is denoted by .

Vectors other than the null vector are called proper vectors.

Unit Vector

A vector whose modulus is unity, is called a unit vector.

The unit vector in the direction of  is denoted by  (read as "a cap").

Like and Unlike Vectors

Vectors are said to be like when they have the same sense of direction and unlike when they have opposite directions.

Co-initial Vectors

Vectors having the same initial point are called co-initial vectors.

Co-terminus Vectors

Vectors having the same terminal point are called co-terminus vectors.

Collinear or Parallel Vectors

Vectors are said to be collinear or parallel if they have the same line of action or have the lines of action parallel to one another.

Coplanar Vectors

Vectors are said to be coplanar if they are parallel to the same plane or they lie in the same plane.

Negative Vector

The vector which has the same magnitude as that of  but opposite direction is called the negative vector and is denoted by −.

Reciprocal of a Vector

The vector which has the same direction but has magnitude reciprocal to that of a given vector.