Inertia? Help! Thanks...they're will be a best answer!?

A MOMENT is found by a weighted sum.

We can have a moment ( used in torque ) of sum F * x ( we have different forces at different distances x)

And a moment of inertia of sum m * x^2 ( we have different masses at different distances x)

the "area moment of inertia" is a badly used term as it has nothing to do with inertia at all.

But it is the sum of elements of area * x^2 ( we have different pieces of area at different distances x from some origin )

Your "mass moment of inertia" is the moment of inertia as shown above.

is sum m * x^2