  The different conventions used in the semiconductor and magnetic metals
communities can cause confusion in the context of spin polarization and
transport in simple heterostructures. In semiconductors, terminology is based
on the orientation of the electron spin, while in magnetic metals it is based
on the orientation of the moment. In the rapidly expanding field of
spintronics, where both semiconductors and metallic metals are important, some
commonly used terms ("spin-up," "majority spin") can have different meanings.
Here, we clarify nomenclature relevant to spin transport and optical
polarization by relating the common physical observables and "definitions" of
spin polarization to the fundamental concept of conservation of angular
momentum within a well-defined reference frame.
