In other words, it is the smallest foot size registered for adults. Practically non-existent, as it is too small for adults and too big for kids.
A very effective filter for a full shoe store to be boiled down to 1-2 pairs immediately.
[I currently live in Japan, and although my feet are only medium in the U.S., I have a lot of problems buying shoes that are big enough here ... they exist, but it's usually the case that if I just choose something I like, the store doesn't stock it or has run out (typically they only get a few pairs of "fringe" sizes). I either have to buy only the most boring and standard shoes (which they sell in large enough numbers to justify carrying fringe sizes) or have to be on a constant lookout for new shipments. As a result, I really hate buying shoes, and often end up wearing them into the ground, getting my feet wet through the holes in my soles when it rains.... TT ]