Drift velocity

The drift velocity is the average velocity that a particle, such as an electron, attains, due to an electric field. Since particles actually accelerate due to an electric field to the speed of light, the term "drift velocity" can only really apply to carriers in materials, and cannot apply to particles in a vaccum. Particles in solids, for example, actually collide or scatter with the lattice (or phonons), which slows them down. In equilibrium they will have an average velocity, and this velocity is the drift velocity.