It's an industry term for cosmetically imperfect gear. You might also see it called "blem stock" or "blemish stock". At Vanguard, "B-stock" mics are still 100% functional and sound just as good as our A-stock mics. The only difference is minor imperfections like micro-scratching, specks of dust under the paint, or a laser engraving that's not as sharp as we'd like it to be. We are super picky about cosmetics, and every microphone is very carefully examined under bright lightning before audio testing. The ones that don't pass visual muster are still put through the full battery of audio and electronic testing, and sound just a dreamy as the A-stock units. They still carry the full 5-YEAR WARRANTY; B-stock just lets you save a few bucks on your new favorite mic!