History and overview
It is the "original" Japanese soy sauce, as its recipe is closest to the soy sauce originally introduced to Japan from China. Technically, this variety is known as miso-damari (味噌溜り), as this is the liquid that runs off miso as it matures.
The Japanese word tamari is derived from the verb tamaru (溜る, 'to accumulate'), referring to the fact that tamari was traditionally a liquid byproduct made during the fermentation of miso.
Comparison to other typs of soy sauce
Tamari is darker in appearance and richer in flavor than koikuchi. It contains little or no wheat. Wheat-free tamari can be used by people with gluten intolerance. Tamari is more viscous than koikuchi.
Of soy sauce produced in Japan, 1.5% is tamari.
Oftentimes, other varieties of soy sauce are inaccurately referred to as Tamari shoyu. The back label in Japan, by law, will clarify whether or not it is actually tamari.