Miso is a traditional Japanese seasoning. It is produced by fermenting soybeans with salt and kōji and sometimes rice, barley, seaweed, or other ingredients.
At its most basic, miso is a fermented paste that's made by inoculating a mixture of soybeans with a mold called koji (for you science folks, that's the common name for Aspergillus oryzae) that's been cultivated from rice, barley, or soybeans.
Miso is the ultimate reference point for the flavor sensation known as umami. The paste and the soup have a deep savory flavor, with toasty, funky, salty-sweet richness.
This umami flavor forms the base of a lot of everyday Japanese cooking.
Miso paste is used for making things such as sauces, dressings, batters, and soups.
When making sauces, dressings, batters, and soups the miso paste is mixed into the sauces, dressings, batters, and soups.
Miso paste can be eaten cooked or raw but it's usually added to the foods after the foods are cooked but sometimes the Miso paste is added before the food is cooked.
The Miso paste adds flavor to the foods that the Miso paste is used in.
When Miso paste is used in the foods the Miso paste adds a salty umami flavor to the foods.
Most Miso paste is used and made in Japan which is where the Miso paste ingredient has been used since the eighth century or earlier.