The definitions I've heard of "high concept," all seem to include "unique," "easy to envision," and "appeals to all four quadrants," the over/under 24 and male/female. In practice, it's really a combination of title and logline that is evocative, succinct, and somehow presents the unique element/s as something of a twist on the known. The 40-Year-Old Virgin: ScriptReaderPro logline: A 40 year old man exposed as a vir­gin, takes up the chal­lenge set by his work bud­dies to sleep with a woman. IMDB logline: Goaded by his buddies, a nerdy guy who's never "done the deed" only finds the pressure mounting when he meets a single mother. The title sets up as much as the logline - though I suspect the logline it went out under was much better than either of these. Just the title, however, sets it up, doesn't it? Drop that title into any roomful of writers and you are going to get some close variation on the movie actually made. That's sort of the beauty of a high-concept idea, the only thing that's not right in your face is why the heck somebody hadn't done it already. Back to the high concept thing though, the concept does fulfill all the criteria. It hadn't been done before. It could be expressed really succinctly, just the title really. It's sex and a comedy, so that's got all the guys, the gals will go along with it because - uniquely! - the virgin is a man instead of woman (and the guy is presented sympathetically), the 40-Year-Old gets you young and mature audiences. Brilliant.

I agree with the comment above - high concept: unique, appeals to a wide audience, and can be stated succinctly - the idea can be said in a title or one sentence and you can see the entire movie before you. That's high concept to me!