Okonomiyaki Flour is a Japanese flour that contains wheat flour and dried, ground Yamaimo powder in it as an added starch for additional binding power, and flavour.
Some brands contain katsuo (powdered bonito) as well.
It is used to make Okonomiyaki. To the flour, you add your ingredients such as cabbage, egg and water to make your Okonomiyaki.
You can also buy instant Okonomiyaki mix, to which you just add water.
Okonomiyaki Flour is generally sold in Japan in 500g and 1 kg packages.
Some people in North America suggest Bisquick as a substitute (sic).