What does the idiom just a hair off mean?

The idiom "just a hair off" is used to describe something that is very close to being correct or accurate, but slightly misses the mark. It implies a small, insignificant difference.

Here are some examples:

* "Your answer was just a hair off, but you were very close."

* "The painting is just a hair off from being perfect."

* "My estimate for the project was just a hair off, but I was still within budget."

Essentially, it means that something is "almost" right, but not quite.