n. 1. vector quantity. any quantity that has both a magnitude and a direction, such as velocity as opposed to speed. 2. an n-tuple of real or complex numbers viewed as a member of an n-dimensional Euclidean space. These are used to represent vector quantities, where the length of the vector is the magnitude of the quantity, and they have the same direction numbers; they are represented in diagrams by arrows in the same direction, of which the length is proportional to the magnitude. Vectors are usually symbolized by bold typeface letters or by arrows or bars above them:

Compare scalar, tensor. 3. an element of a vector space.