Drift velocity describes the overall velocity of a particle that moves continually and changes its velocities and directions randomly. This velocity is best understood when imagining the free electron movement in a conductor.
In a conductor, free electrons move in random directions and with random velocities. The randomly moving electrons in a conductor are affected and move along the electrical field direction when an electric field is applied. Although the electrons continue to shift towards superior potential, they do not stop their random movement due to the electric field. Therefore, each particle attains an average velocity as it moves along the greater potential end of the conductor.