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.
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").
Vectors are said to be like when they have the same sense of direction and unlike when they have opposite directions.
Vectors having the same initial point are called co-initial vectors.
Vectors having the same terminal point are called co-terminus 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.
Vectors are said to be coplanar if they are parallel to the same plane or they lie in the same plane.
The vector which has the same magnitude as that of but opposite direction is called the negative vector and is denoted by −.
The vector which has the same direction but has magnitude reciprocal to that of a given vector.