Moment of inertia (MOI) in physics, quantitative measure of the rotational inertia of a body i.e., the opposition that the body exhibits to having its speed of rotation about an axis altered by the application of a torque (turning force). 
The axis may be internal or external and may or may not be fixed. 
For point mass Moment of inertia is simply the mass times the square of the perpendicular distance to the axis of rotation. 
⇒ I = m × r 
where I is the Moment of Inertia, m is point mass, r is the perpendicular distance from the axis of rotation.