I'm partially glad this post got bumped. I actually find it very discouraging that this question got closed. It's the type of questions that, in my opinion, gets accidentally closed because of our (rather just) impulse to close off-topic questions.
Definitions in the sciences, and especially, contrary to how one of the responders here says, in the "open problems" in science, requires a high degree of help from philosophy (in the case matter, phil-of-physics).
It's the case (almost) everywhere in science where a new idea comes to light, it need be highly articulated and well-thought. Much of the work sometimes being done by the scientists themselves (hopefully with some basic knowledge of the underlying philosophical implications), but that doesn't mean it isn't a philosophical work.
Specifically this subject matter, quantum theory in general and locality in particular, has a very robust philosophical work that attempt to ground, define, and speculate on. For example, an entire article on SEP specifically on this - https://plato.stanford.edu/entries/qm-action-distance/.
It's a shame I haven't seen this post when it was posted, else I'd have voted to reopen it. But I hope we can learn from this.