Futomomo
“thigh” — the body part, used as the name of the tie
A tie binding a folded leg, calf against thigh, used as a shape in itself and as a suspension attachment.
The name is simply the Japanese word for thigh. The tie folds the leg at the knee and binds calf to thigh with a series of wraps, producing a compact shape that holds well under load.
It appears early in most curricula because it is useful and relatively forgiving, and it recurs constantly in partial suspension, where it is one of the standard points to lift from.