What is the meaning of the idiom 'by the skin of his teeth'?

if you are successful but only by the skin of your teeth it means you barely did it. You can win a game by the skin of your teeth, pass an exam by the skin of your teeth or you can beat a red light by the skin of your teeth. You still win but only by the smallest of margins.
Just barely, very narrowly, as in Doug passed the exam by the skin of his teeth.

A related term appears in The Bible (Job 19:20), where Job says, "I am escaped with the skin of my teeth," presumably meaning he got away with nothing at all. Today the phrase using by is used most often to describe a narrow escape. [c. 1600]

If you do something by the skin of your teeth, you only just manage to do it, and come very near indeed to failing.