Alex Ross, the music critic of the New Yorker and freshly minted genius — courtesy of the MacArthur Foundation — marks the release of the paperback version of his prizewinning book “The Rest is Noise” with a new online musical glossary, complete with audio examples.

If you’re shaky on what a fugue, adagio, diminished chord, or “12-tone” system is — or, more basically, what makes a minor chord different from a major chord — this is the place to go (and to listen).