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There really cannot be a grey area; either you cheat, or you don't.
Personally, while I don't like black hat, I can at least respect their honesty, and even envy the courage to take risks with their income.
Grey Hat? The Spam That Dare Not Speak Its Name ;)
Black Hat vs. White Hat vs. Gray/Grey Hat = Perpetual Black Eye for SEO
Since you've not heard of it before, just move on. Try not to make it part of your "Marketing Speak". You may end up looking less than Professional. < That was not intended for anyone in particular. I know I'm going to get raked over the coals right now but hey, I'm prepared. ;)