The literal translation of umami
means the "pleasant face" that one shows when eating food with this so-called 5th taste. Umami can be defined as the taste sensation that is elicited by certain amino acids notably glutamate, guanosine, and inosine.
It can be said that one guiding principle in Japanese Cookery encourages its practitioners to attain a balance of umami from the many different sources.
Tomato and Konbu for example, are great sources of glutamine which contributes to the taste sensation umami. Mushrooms have guanosine which also gives a distinct umami sensation. Animal products, most notably Katsuoboshi, are great sources of inosine which gives yet another dimension of the multifaceted thing of beauty which is umami.
Knorr liquid seasoning has all three in a very balanced and agreeable amounts, hence its popularity as a generic seasoning.
These are just the major notes that contribute to the symphony of taste. To limit yourself to these sources of umami would be akin to listening to a melody while having many other sources can lead to a deeper eating experience which would be more like listening to a complete orchestra perform a musical piece with all the undertones and nuances of the many flavors.
The cuisines of the world have different levels of understanding of umami, or at the very least, very different amounts of written records of their understanding of the same. The French have a love for truffles and the umami they provide but I know of no direct reference to the concept of umami aside from Escoffier's brief mention of a thing he called osmazome. The fact that the French method of making tomato concasse invovles squeezing out the seeds and the gel that surrounds it convinces me that the french have a very low regard for umami, choosing other methods to attain quality in their cooking. The gel like substance surrounding the seeds in a tomato have a good amount of glutamine. The Italians have a better understanding of umami and it is no surprise that next to Japanese cuisine, Italian is the next most popular cuisine in Japan.