Like the others who have answered this, I have never heard this term either. I can imagine (most likely incorrectly) what it might refer to - If you look at Bed-Stuy on a Google map, you will see a large area in the center that has no nearby subway service. Largely because of this, that area has not gentrified the same way as neighborhoods like Williamsburg and Bushwick. There are lovely buildings in that area (some of nicest in NYC!), but they are not desirable because it takes a long walk to get to a subway into Manhattan.
Just a guess...