What is meant by the term "B stock"?

I know this has come up before, but I'll be darned if I can find it. So. exactly what is meant "B stock"? Are these re-furbished units,or re-manufactured units? What would qualify a unit to get this rating?
I purchased a Yamaha DSP-A1 in gold, a "B stock" item at a substantial savings over a year ago, and the thing has run flawlessly and looks the same ever since I bought it. At the time, the dealer told me that these could have cosmetic blems, but neither he, or I could find any. Just curious whether these deals are worth it, and when selling the unit, must this be disclosed?
Thanks for any info.