To me a reach is a guy who is drafted significantly higher than he should have gone. It's hard to pinpoint because it's subjective.
it drives me crazy though when people call a guy a reach and then say how that guy should have gone about 5-10 spots later. Guess what, we don't ******* pick 10 picks later. We pick NOW and while you'd love to be able to trade back and still get your guy, you can't assume that's possible.
So if the steelers draft a guy at 20 and people criticize by saying that guy shouldn't have gone until the end of rd 1, that's bullshit. If you rate a guy and he's the top guy left at a position of need and none of your other options at that pick are rated significantly higher, then it's not a reach.
Here's 2 examples
Terrell Edmunds - some said he was a reach. He wasn't. The top ILBs were gone, so Safety was the only position that made sense here and Edmunds was the top guy on their board. Could have have gone 10 spots later? Maybe. But he probably would not have lasted until the steelers pick in rd 2.
Troy Edwards - steelers needed a WR. The top 2 guys Tory Holt and David Boston were gone. Troy Edwards was the next rated WR. The difference here is that Jevon Kearse was still available. Kearse was perfect for the 3-4 defense and as we know from Cowher essentially demanding Donohoe be fired over this pick, Kearse was much higher rated on the steeler board than Edwards. That's why Edwards was a reach.
Reach come down to 2 questions
1 Will the guy be available at your next pick?
2 Are you passing up a much higher rated player on your board?