Wikipedia Article About Dashi on Wikipedia
Dashi (出汁, ダシ) is one of several simple soup stocks considered fundamental to Japanese cooking. The most common form of dashi is a simple broth or stock made by heating kombu (edible kelp) and katsuobushi (flakes of dried bonito) in water and then straining the resultant liquid. Dashi forms the base for miso soup, Japanese noodle broth, and many Japanese simmering liquids. Fresh dashi made from kelp and katsuobushi is rare today, even in Japan. Most people use granulated or liquid instant substitutes.
Other kinds of dashi stock are made by soaking kelp, shiitake, or niboshi in water for many hours or heating them in water nearly to boiling and then straining the resultant broth. Kelp stock or konbu dashi is made by soaking kelp, or sea tangle, in water. Shiitake dashi stock is made by soaking dried shiitake mushrooms in water. Niboshi dashi stock is made by soaking small dried sardines (after pinching off their heads and entrails) in water.
Other important Japanese flavors include shoyu, mirin, rice vinegar, miso, and sake.