Reading other questions I see that a quote by Arthur C. Clarke - "Any sufficiently advanced technology is indistinguishable from magic" - is often being treated as an axiom. However, in a world where magic is developed side by side with technology, there must be a strict difference.
What that difference is? There could be worlds where all magical powers come from one single source - that allows us to call them "magical". Another simple version - technology exploits the laws of nature, magic breaks them.
In less trivial cases, how "magical" could be defined? What is the guiding principle that could let us actually distinguish technological achievements from magical ones?
For them who say the answer is heavily depended on how magic works in a particular world - no it is not. In a sci-fi world we don't know the ways how technology work, but we still call it "technology". The same must concern "magic" as well.