A "clone" is a game in the style of. Like say you create a game that plays and looks like Asteroids. That's a clone. Now, what's gets tricky is the fact that I wouldn't consider creating a game of today in such a fashion. You can take alot from a game from today and put it in your game, but there are so many intricacies in today's game it wouldn't technically be a clone. It would be a rip-off, but I'm not saying that in a bad way. Most games of today are rips of each other.
I hope I'm answering that somewhat. I think it's just my personal opinion, though.
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