What does the saying 'by the skin of your teeth' mean?

It's similar to just getting by- getting what you want in the last minute. For example, at the derby two horses cross the finish line within hundredths/thousandths of each other. The horse that one would have "by the skin of his teeth."

It means barely. As in; He barely won the race or He barely passed the test. He won the race by the skin of his teeth. He passed the test by the skin of his teeth. It does not mean, just getting by. Barely getting by, yes.
just barely made it