The Kerr metric is appropriate for describing black holes with a nonzero value for this quantity and zero charge.  
The Feynman disk paradox can be resolved by noting that the electromagnetic field is allowed to carry this property.  For light, multi-electron atoms, spectral details are correctly reproduced by Russell-Saunders coupling of this property of the electrons.  The Kerr metric is appropriate for describing black holes with a nonzero value for this quantity and zero charge.  The Bohr model of the atom proposes that this quantity is quantized in units of h-bar.  FTP name this quantity whose time derivative is the torque, given by the moment of inertia times the rotational velocity, which comes in orbital and spin subtypes.
The Feynman disk paradox can be resolved by noting that the electromagnetic field is allowed to carry this property.  
angular momentum