Miso is soy bean paste, which is an essential condiment in Japanese cooking. Miso is made by fermenting soy beans with salt and koji. Koji are cultured grains such as rice, barley, and soy beans.
There are so many kinds of miso available from different regions in Japan. The color can be darker or lighter, and the taste can be sweeter or saltier. The most common kinds of miso are shiro (white) miso and aka (red) miso. The white varieties aren't really white, but are light yellow and have a sweet taste. The red varieties are dark brown and said to have savory flavors. Shinshu miso (brown miso made in Shinshu region) and inaka miso (barley miso) are also popular. Awase miso, which are mixtures of differet types of miso, are popularly sold at stores.
In Japan, miso is used not only for miso soup but also for marinating fish, sauteed dishes, ramen, pickles, and more.