The term I_xx, I_yy and I_zz are called the mass moment of inertia of the body about the x, y and z axes respectively. Note that in each such case, we are integrating the mass element , times the perpendicular distance squared from the mass elements to the coordinate axis about which we are computing the moment of inertia.

I_xy, I_xz and I_yz are called mass product of inertia about the pair of axes given by the indices.

It is clear that,

I_xy = I_yx , I_xz = I_zx