"Any sufficiently analyzed magic is indistinguishable from science."If your primary criterion for "magic" is that it not be understood, then what qualifies as magic is highly subjective and depends very much on whether a magic user is a major viewpoint character and how much any such characters understand what they are doing. Furthermore, it can change purely by in-world research or the addition of one scene containing a monologue about how it all works. Shift around a few characters and insert monologues, and just about any fantasy series could be converted to scifi rather easily. I think this is a rather poor and unsatisfying definition, as the definition of something should not in my opinion depend on how much of it is revealed to the reader.
I haven't really formalized the definition of what I consider magic, but I think the irreplaceable involvement of the magic-user is an important criterion, possibly the most important. If it's something that is done by a particular person, and there are people who, regardless of mental capacity, real-world physical characteristics, and education, would be completely incapable of replacing that person even in theory in doing it, then it's probably magic. Inventing a computer? Get enough smarts and the right education, and anybody could do it. Shooting coins around with Allomancy? Sorry, if you're not a Mistborn or the right Misting, you can't do it. Any exercise of Mind-
Directly-over-Matter or similar usually qualifies too, even if everyone in the setting is technically capable of learning it. By my definition, Allomancy and Feruchemy are most definitely magic systems. Now that I think about it, Hemalurgy is more borderline, but I'd still call it magic due to how its interaction with the definite magic systems is such a major part of it.