Mathematically, a vector is a quantity, defined by both magnitude and direction. For example, a vector could be illustrated by an 1 inch arrow pointing at a 30 degree angle. Another vector may be 2.5 inches and point at a 160 degree angle. In the computer world, vectors are used to define paths in certain types of images, such as EPS files and Adobe Illustrator documents. These images are often called vector graphics since they are comprised of vectors, or paths, instead of dots. Vector graphics can be scaled larger or smaller without losing quality.

In computer science, a vector may refer to a type of one dimensional array. For example, a vector called "fibonacci" that stores the first six values of the Fibonacci sequence would be defined as follows:

fibonacci[0] = 0, fibonacci[1] = 1, fibonacci[2] = 1, fibonacci[3] = 2, fibonacci[4] = 3, fibonacci[5] = 5

Vectors are similar to arrays, but unlike arrays, vectors use their own memory management mechanisms. Arrays are restricted to the memory structure supplied by the programming language they are created in, typically called a stack. Vectors have a more dynamic structure, often referred to as a heap, which gives them greater flexibility in how they use memory. While an array uses a static amount of memory, the memory used by the vector can be increased or decreased as elements are added or removed from the vector.