It was a short way of writing a different spelling of the words all correct. Some foreign-born people wrote all correct as o-l-l k-o-r-r-e-c-t, and used the letters O.K.

VOA: special.2010.02.28

So where as I currently am manually typing like dash L cs50 and dash O hello.

刚刚我们提到自己动手敲,一些像/lcs50还有/0，hello这样的命令。

哈佛公开课 - 计算机科学课程节选