A girl's close male 'friend' that she sleeps with when her self esteem is a bit low. Usually an ex. The guy that every significant other should beware of any time he screws up even slightly. You'll know which one he is because she'll talk about him like you'll never be quite as charming/good in bed/sensitive/etc. as he is.
"Her boyfriend looked at another girl at the mall, but she felt better after she hooked up with her Josh." or "Hey man, that guy's her Josh... when she starts hanging out with him again you might as well just pack your stuff."