So, where did all this leave me, besides "in a stupefied state"? I inferred that "high concept" meant a story whose idea was taken to an extreme. But that still seemed pretty vague to me. Off to the magical internet in search of useful blogposts to which I could refer any loyal, or newly arrived, readers.
Many of the links I found are directed towards scriptwriters. Turns out "high concept" is a Hollywood term that has made its way from films to books. That realization took me a long way towards an understanding of "high concept" applied to books. It means "blockbuster movie potential."
Perhaps that's just a tad cynical. For more in-depth explanations, here are a few links: My favorite, from a non-script-writer perspective, is the one at FictionMatters. This explanation is fairly simple, acknowledges how annoying and befuddling this term can be, and speaks to us book types and the darker anxieties this term might stir up. If you want the scriptwriter's explanation, try Writers Store, Absolute Write, or The Dark Salon, among others.
Personally, I'd like to see "high concept" and "literary fiction" thrown into the bin of overused and useless terms. But that's just petulant little me. Got any terms you'd like tossed in with them?