Ownership is probably most useful as a legal term. You can legally "own" something. That ownership is absolutely temporary because you can't take it with you.You can't truly own anything. You can be the care taker for awhile at best. Perhaps not in line with the motivation behind or tone of the thread, but your mortality insures this to be the case.
In a practical sense, ownership is what you have in your possession as long as you can keep others from taking it.