For those too lazy to educate themselves, Umami
is the "savory" taste. It's somewhat of a meaty/fishy flavor and is found in tomatoes (that's probably why many people like ketchup), mushrooms (especially dried), green tea, soy sauce, fish, and other food items. In high concentrations, it crates that "asian food taste" that many people enjoy. MSG is an artificial glutimate which attempts to emulate the umami taste of the traditional Japanese Dashi
stock. However, it happens to be a little easier to prepare (and cheaper).