It seems as though many of the threads on this site deal with issue of what the concept of "spin" actually means. I think it may be useful to devote a thread designed to solicit out of the community just what this property of fundamental particles is. Intrinsic angular momentum as opposed to orbital angular momentum? What does that mean? Is something actually spinning, or are we to treat this avisually and just as an abstract measure..simply a quantum number? And, perhaps most interestingly, what is this property of spin, in particular the 1/2 h-bar spin of the electron, that drives the marriage of two electrons in any given atomic orbital? What is the property of spin that drives these two electrons to co-exist in that sort of harmony, and how does that manifest in the creation of and integrity of an atomic orbital? Finally, can an electron change its spin from the up state to down and vice versa? More specifically, what are the conditions that drive this change and what are the mechanics that make it happen?