Hi, In many quantum physics books I see questions such as "what is the spin-orbit interaction in this case?" Sorry if this seems like a dumb question, but what do they mean by this? Do they mean the ENERGY of the spin-orbit interaction or something else? Also, could anyone give (or write a weblink for) the spin-orbit interaction? I searched a few books and online lecture notes from various universities, but I couldn't find anything conclusive.