Page "Angular momentum" Paragraph 33

The first term is just the angular momentum of the center of mass.

It is the same angular momentum one would obtain if there were just one particle of mass M moving at velocity V located at the center of mass.

The second term is the angular momentum that is the result of the particles moving relative to their center of mass.

This second term can be even further simplified if the particles form a rigid body, in which case it is the product of moment of inertia and angular velocity of the spinning motion ( as above ).

The same result is true if the discrete point masses discussed above are replaced by a continuous distribution of matter.