It's something that someone else wrote or maybe you wrote, but you can encapsulate all of your ideas or your functionality inside this thing called a function.

它是别人或你自己写的，但是你可以压缩你所有的想法,或者你这个东西里面的功能叫做一个函数。

哈佛公开课 - 计算机科学课程节选