Designers make different types of collections & somethings when it is really exclusive they refer to them as their black label brand. It's usually an obscene amount of money more than usually, as in an Oscar De La Renta dress for 3,900 dollars & a black label dress would be 12,300. The difference is noticable & those that know about it, are the ones that can afford it.
"Darling, look, it's Jimmy Choo's black label, there's only three pairs left?"
"Marc Jacobs makes all sorts of cheap clothing & accessories, but to find his black label you need the third floor in Saxs in NYC."