subniche
noun
sub·niche 
ˌsəb-ˈnich,
also -ˈnēsh,
or
-ˈnish variants or sub-niche
plural subniches or sub-niches
: a portion of a niche (such as a part of a specialized market)
Because ebooks are digital, Amazon can afford to give each subniche (where there might only be 20-30 books) a bestseller count.
Dennis Posadas
Dennis Posadas
Word History
First Known Use
1989, in the meaning defined above