Definition of Terms
Distance (d) is the gap between any two points in space. It is the total movement of a body regardless of the direction. It is a scalar quantity measured in meter (m). Distance is the product of average speed and time. That is:

Distance = average speed x time = st

Displacement (X) is the distance covered in a specific direction. It is the change in position of a body. Displacement is a vector quantity measured in meter (m).

Displacement = average velocity x time = vt

Speed (s) is the total distance (d) covered over a period of time. It is the rate of change of distance with time. That is:

Speed = distance/time = d/t

Average speed is the ratio of the total distance travelled and the total time taken. It is a scalar quantity measured in m/s.

Average speed = total distance travelled/total time taken

Velocity (v) is the displacement (x) of a body in a given direction over a period of time. The velocity of a body is the rate of change of its position with time. That is:

Velocity = displacement/time = x/t

Acceleration (a) is the rate of change in velocity of a body with time. It is a vector quantity.

Acceleration = Change in velocity (ΔV) / change in time (Δt) = v-u/t

A body is accelerated only if a net external force acts on the body, and the acceleration produced is inversely proportional to the mass. That is:

Acceleration = force/mass = f/m

Retardation (ar) is the decrease in rate of change of velocity. It is also known as deceleration or negative acceleration. It is measured in ms-2

Retardation = decreasing velocity change/time taken

Instantaneous velocity is the velocity at any specific point in time.

Instantaneous acceleration is the acceleration at any specific point in time.