Shoyu is simply the Japanese word for soy sauce, and generally refers to the kind commonly used for cooking and as a dipping sauce. The main soy sauce ingredients include soybeans, wheat, salt, and water.
Depending on the dish that you are preparing, different kinds of soy sauce bring out different flavors. Koikuchi shoyu (regular soy sauce) accounts for around 80% of the soy sauce produced in Japan, other types include light colored soy sauces such as usukuchi shoyu and shiro shoyu, saishikomi (a double brewed soy sauce produced mainly in the southwest of Japan) and tamari shoyu, known for its thickness, rich umami, and savory flavor and fragrance. The five elements that contribute to the taste of soy sauce include saltiness, sweetness, acidity, bitterness, and umami.