HDTV T.V HELP!!! Built in Tuner V.S HD Ready whats the difference

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i saw a really good deal at best buy on a hdtv hd ready tv. i was going to get it, but i didnt know what the (ready) in hd ready meant....... the dude at the store was like this one is better quality, but was a lame guy and left the info at that...bad salesman eh? anyhow can anyone tell me what is the difference? why was that guy against that tv?