free.board

n.（名詞）
Nautical The distance between the water line and the uppermost full deck of a ship.
【航?！?/i> 出水高度：船的吃水線與最高層甲板之間的距離
The distance between the ground and the undercarriage of an automobile.
離地間隙：從地面到汽車底架之間的空間

來源：
Probably ultimately partial translation of Anglo-Norman franc bord [land claimed outside the fence of a park or forest]
可能最終為 英法語 franc bord的部分翻譯 [索取的公園或森林的邊界之外的土地]
franc [free]
franc [自由的]
bord [border]
bord [邊界]