详细解释:n. 信封, 封套, 封袋
【医】 膜, 包袋
英语解释：
名词 envelope:
a flat rectangular paper container for papersany wrapper or coveringa curve that is tangent to each of a family of curvesa natural covering (as by a fluid)the maximum operating capability of a systemthe bag containing the gas in a balloon同义词：gasbag