A vector whose modulus and direction do not change with the change of spatial coordinates is a constant vector. A unit vector is a vector whose modulus is equal to 1. Since it is a non-zero vector, the unit vector has a definite direction. There are countless unit vectors.

In mathematics, vectors (also known as Euclidean vectors, geometric vectors and vectors) refer to quantities with magnitude and direction. It can be imagined as a line segment with an arrow. The arrow indicates the direction of the vector; Line segment length: indicates the size of the vector. Only the magnitude corresponds to the vector, and the quantity without direction is called quantity (called scalar in physics).