Velocity is a measure of how fast something moves in a particular direction. In other words, a velocity is a speed with a direction. For instance, if an object moves east at 9 metres per second (9m/s), we would say that its velocity is 9 m/s to the east.
Gradient The formal definition of a concentration gradient is the process of particles, which are sometimes called solutes, moving through a solution or gas from an area with a higher number of particles to an area with a lower number of particles. The areas are typically separated by a membrane.