Small, very small, tiny, or so-small-it's-almost-non-existent Japanese bar
or drinking establishment
, almost always run with an iron rule by the owner/master of said establishment.
Nomiya are no-nonsense drinking holes, often appallingly lit and decorated, but serving a very important role of community for the regular guests that frequent the establishment.
Nomiya can be very intimidating for the neophyte foreigner, since many are not much larger than your front room and may only accomodate a half-dozen drinkers. Imagine all those eyes on the strange gaijin! /-)
For a comparitively less stressful drink, check out the larger izakaya where you can get some good eats to go with your drinks, and can be somewhat more anonymous!
For the brave, visit the infamous Shomben Yokocho (or "Piss Alley") in Tokyo's Shinjuku district for a taste of ultra-nomiya.