I keep here this, its over bored, whats its mean???

The cylinder is bored out to a larger size. Many times they bore it .030" larger than it was, (if you hear "It's bored 30 over" that's what it means). Of course there are many other bore increases. When you bore an engine out, it's usually because it has a lot of miles on it and the cyl. wall isn't even anymore. If you bore an engine out, you'll need a new set of pistons in that bore size. Occasionally you might see a big bore engine that the person bored it out for more displacement, but that's not nearly as common.