Velocity of an object refers to the rate of movement or change of its position in terms of distance covered as well as the direction of movement. In contrast, speed is a measurement of the rate of change of position. A variable or quantity like velocity that has speed as well as direction is called a vector. A variable or quantity that has only magnitude is called a scalar quantity.
The magnitude of velocity and speed are measured in the same units such as 'meters per second, or 'kilometers per hour'. The magnitude of velocity and the speed of a body is same when the movement of the body is in a straight line, and there is no reversal of direction of movement due to acceleration.
When a object moves along a curved path at a constant speed, the velocity is not constant but variable. For example, an object moving along a circle of radius r at constant speed of x meters per second will have a variable velocity due to an acceleration equal to (x^2)/r m/s^2 acting towards the center of the circle.
Velocity is a vector that points in the direction the body is moving and has a magnitude which is equal to the rate at which the body is moving or the distance travelled by the time taken. This could be in meters per second, kilometers per hour or the alike.
Speed on the other hand is a scalar quantity that is equal to the distance travelled divide by the time taken. A vector cannot be equal to a scalar. In some cases though, the magnitude of velocity may be equal to the speed.