A grey hat is some one with a mixture of black and white hat experience. Usually, a grey hat is someone who performs network security or system security analysis for organizations.
BOB the grey hat will scan your webserver for vulnerabilities for x amount of $. When he gets home he will reverse engineer microsoft products using stolen windows code.
Someone who works on the computer, especially hacking that hacks into systems not to look for anomalies or to destroy a system. They're basically in there screwing around causing minor or no damage.
A Grey-Hat is a term given to Gandalf the grey by some stupid idiots who think that he is a computer Hacker
Gandalf the Grey-hat