call it a day 这个短语是大学惯用法上学的 😚字面上的意思是:叫做它一天吧.引申意思就是"就这样结束了"“收工了”."不再干下去的了"。这个可以适用于开会，上课结束后。
下面来自VOA的解释
Call it a day!

When you "call it a day" in American English, it means you are ending work, play, or something you are doing that day. Often, it means you have finished your work, and you are going home.

You can use this phrase in any situation, and everybody in America will understand you.