clearance

详细解释:n. 清除, 间隙
【化】 间隙; 空隙
【医】 清除, 清除率, 廓清率; 间隙

英语解释：

名词 clearance:

the distance by which one thing clears another; the space between themvertical space available to allow easy passage under something同义词：headroom, headway