Coincidentally enough, when I was asked this question in the interview, this is how I answered:
Q) I don't think there's a right answer to this... but you've mentioned rulings over rules, danger and zero to hero. Is that how you define OSR? Is there an accepted definition?
I don't think there is any "one true way" to define the OSR, because the OSR above all else is meant to emulate the feel and/or mechanics of many games from the 70s/80s. Since there were so many games even then, there is no real way one could define the OSR objectively. That said, I think most fans of the OSR would agree on common themes. Those being rulings over rules, zero to hero, mechanically more lethal of a system, sandbox play, etc. Because gaming was still new back then, and we didn't have the internet where you get an instant answer to a question by the design team, most tables were coming up with stuff on the fly. That fostered a lot of creativity and homebrew. Players were encouraged to come up with their own stuff. I know this is anecdotal, but it seems that there are fewer GMs today who are creating their own game worlds and adventures than in the 80s, where nearly everyone I met was doing that.
So not the best answer, but at least I mentioned how there isn't any one true way of defining it, which I think is the important part.