Velocity is the simplest measurement of speed in a linear direction during a given time. An object, moving in a rectilinear motion, is timed; its velocity is calculated by dividing the distance from starting to finishing point by time required. Velocity is a quantity, related to speed and distance. It is expressed as X feet per second, or X miles per hour.
The units of velocity may be feet per second, feet per minute, or miles per hour. Strictly speaking, velocity of a moving particle is a VECTOR quantity which indicates both direction and speed of MOTION. Thus, when one speaks of the velocity of the wind as 15 miles per hour, he must also state from what direction the wind is blowing.
When the physicist uses the word speed, he refers to non-vector motion; that is, speed is change of position of a body, but without regard to direction.