Source: In common use
Hyoshigi-gitae (拍子木鍛え) is a Japanese sword construction that joins a high carbon piece of steel for the edge with a lower carbon spine.
Hyoshigi are Japanese clappers that look like two beams of square cross-section. It refers to the start of this forging process where steels are laid out like beams and then forged together. How much hagane (edge steel) is used varies, see illustration.
Commonly seen in older Yamato school work. The Yamato school is the oldest of the five traditions of the Kotō period.
See the tsurikomi article by the Kashima sisters.