A benelovent hacker - someone who enters the computer security fray on the side of good. Generally implies understanding of and possibly even use of methods of defanging computer and/or network security, but only done with the consent of the owner of the computer or network in question, either to help them get themselves out of a lost-password type of bind or to audit their security.
Refers to color-coded hats in old western movies: bad guys wear black and good guys wear white. Contrast with black-hat, script kiddie. These are not FreeBSD-specific terms, but they're included here because the terms are relevant to any security discussion.