Vertically means that every class connected to the next class is connected to every class throughout the semester around a spiral.

纵向意味着每一节课都和下一节课有关系,和整个学期内的每一节课都有关系，呈一个螺旋状。

哈佛公开课 - 幸福课课程节选

Yeah, it's great. Actually, no, two to three concerts per semester.

确实，这非常棒。噢，不对，是每学期两到三次的音乐会。

积极参与俱乐部活动 - SpeakingMax英语口语达人

See this happens every semester that the chuckles, the grimaces, kind of roll through the crowd as people catch on, but there you go.

每学期学生们看到这，就会偷笑或者做鬼脸之类的，不过你们随意。

哈佛公开课 - 计算机科学课程节选