the sum of the products of the mass and the square of the perpendicular distance to the axis of rotation of each particle in a body rotating about an axis.

British Dictionary definitions for moment of inertia

moment of inertia

noun

the tendency of a body to resist angular acceleration, expressed as the sum of the products of the mass of each particle in the body and the square of its perpendicular distance from the axis of rotationSymbol: I

A measure of a body's resistance to angular acceleration, equal to the product of the mass of the body and the square of its distance from the axis of rotation. See also angular momentumtorque.