Miso is fermented soybean paste that is a staple ingredient in Japanese cooking. It has a consistency similar to peanut butter, and a strong, salty flavour (although low-salt varieties do exist).
Miso is the main ingredient in Miso Soup, obviously. You can also add miso to sauces, marinades and dressings, or use it as a seasoning to add flavour to dishes. Miso is available in a variety of colours and flavours, ranging from light-coloured and mild, to dark-coloured and pungent.
Miso is a good source of probiotics and is easy to digest. Try to buy organic miso, which is found in the refrigerated section of Japanese markets and health food stores. The organic versions generally contain about half the amount of salt as regular, shelf-stable versions.