In my case, it means I was diagnosed late in life with borderline sweat chlorides. I have heard other "definitions" from other people. I don't think there is a standard definition. I used to refer to myself as having "mild CF" but was attacked on a CF list for saying that, where it was apparently politically incorrect. I was told the acceptable term is "atypical CF". In the interest of having my head handed to me on a platter less often, I try to stick to that term.