Definition
Pubic hair.
See Also
How People Actually Use It
A euphemism for "pubic hairs," itself in this context a euphemistic metonymy for "balls". It is used mostly in expressions such as "to have someone by the short hairs," which is to say "to have someone in a very difficult or hopeless situation," equivalent to "to have someone by the balls."
"It was a real Catch 22! They had me by the short hairs, and they knew it."
Source: Urban Dictionary