Learner's definition of X
—
used in the past as a special mark to indicate that no one under the age of 17 in the U.S. or 18 in the U.K. was allowed to see a particular movie in a movie theater*X级（过去的影片分级用语，美国17岁以下、英国18岁以下青少年不宜观看的电影的标记） — compare g, nc-17, pg, pg-13, r; see also x-rated