gomai

Etymology
literally, 5 sheets

Noun

 * 1)  A construction method for Japanese-style blade steels, composed of 5 layers of 3 steels, with a core, sandwiched by another steel, sandwiched again by another steel. The sandwiching may be two sheets, or traditionally one sheet folded over as a taco.
 * 2)  A steel sandwich made by this method, before and after being welded.