長側 Long Side or Nagakawa
What is Nagakawa of Samurai Armor?
This refers to the part of the small armor plates that are continuous from the front body to the back body, starting from the hinge part. In the modern armor (Tousei Gusoku) using hinges, the hinge part becomes the starting point. Since it surrounds the abdomen, it can be said to be the most important part in the chest armor (Do) (Yoroi).
Image Source https://www.touken-world.jp/word-armor/parts/page/5/
See more terms related to samurai armor in this samurai armor glossary