Niboshi

Niboshi , often called iriko (炒り子) in Western Japan, are Japanese small dried fish. They are one of many varieties of small dried fish used throughout Asia in snacks, as seasoning for soup stocks, and in other foods. The types of fish used in making niboshi vary, including anchovies, sardines, round herring, Pacific sand lance [ja] and others. Niboshi made of anchovies are the most common. The translation of the term "niboshi" is an object of confusion among Japanese speakers, in terms of whether it is sardines or anchovies, because in Japanese, both sardine and anchovy are referred to as "iwashi"(イワシ). The word niboshi 煮干し literally means "boiled" or "dried", and it does not include the specific name of the ingredient. For this reason, niboshi is translated both as "dried sardine" and "dried anchovy". In Japan, niboshi dashi is one of the more common forms of dashi. It is especially popular as the base stock when making miso soup. Niboshi dashi is made by soaking niboshi in plain water. If left overnight or brought nearly to a boil, the flavor of niboshi permeates the water to make the stock.

Source: Wikipedia