I've now updated my About page to give a long-form explanation of what the Long Tail means, with the helpful outboard support of this excellent Wikipedia entry.
Defining the Long Tail is relatively easy to do with the visual aid of the chart at left. But as I discovered at Davos, where I typically had to do the explanation in 10 seconds over the din of a cocktail party, it's still hard to do quickly with words alone. Phrases like "how technology can let us find potentially huge markets for previously sub-economic products" don't do it. What's "sub-economic"? Out of context, it's not even clear what I mean by "products". An example or two makes it all clear, but a great definition shouldn't need one.
Fortunately, I've got some excellent suggestions here, which are a big step in the right direction. I hope to embrace and extend them soon, with a result good enough to be cocktail-party safe.