iriko, myulchi, dried baby sardines, dried baby anchovies.
Niboshi are baby sardines (anchovies by some translations) that have been boiled once then dried. They vary in size from about 1.5" (pictured below right) to over 3"(pictured below left) long with the smaller ones having a milder flavour. They're used in both Korean and Japanese cooking as a flavouring for stock or cooked as a snack.
What's it taste like?
As you might imagine, dried sardines have a very bold flavour. They're not "fishy" in a bad sense, but you definitely get a taste of the sea, and they have a sweet, slightly cedar-like aroma. Because they are full of umami-rich glutamates, they make a good addition to stocks and sauces that need a little more oomph.
Where do I get it?
They typically come in small to medium sized bags and can be found at almost any Asian grocery store in the dried food section. There aren't any other dried fish (that I know of) that have the same shape and size as the ones in the picture above, so they shouldn't be too hard to find.
When is it best?
Because they are dried, there is no season, but they can go rancid if they are very old, so check for an expiration date and don't buy them in a store that doesn't look like they sell much of them. They should be roughly uniform in shape and size and should be mostly whole.
How do I use it?
In Japanese cuisine they are typically used to make dashi which is the basis of almost every soup (from miso soup to udon soup) and sauce in the Japanese food repertoire. Because of it's bold flavor, niboshi stocks are typically reserved for heavier soups and dishes with katsuobushi or kombu being used for lighter stocks. Niboshi dashi is commonly used in stock for udon, kakuni, and red miso soups. It can also be stewed with soy sauce, mirin and sugar to make tsukudani which is an accompaniment for rice. Seasoned and dried, they're often eaten as a bar snack with almonds and rice crackers.
In Korean cuisine, myulchi are fried with peppers, soy sauce, sugar and sesame oil to make a type of banchan. They are also used to make stocks for various soups and stews.
High in calcium when consuming the whole fish.