Within the context of flat or reverse cambered skis, "greasy" refers to a feel that the ski is not very directionally stable or sort of "indecisive". This occurs at lower edge angles and in turn transitions. This is most notable when the ski is in and out of the snow as in mixed conditions. When the ski is fully submerged in 3D snow it is usually not very noticeable. At higher angles the ski engages and stabilizes minimizing the feeling. Tastes vary on this greasy feel. IOW......some love the feel, some hate it, some are in betwixt. I'm in the latter camp in that I can tolerate the "greasiness" on some skis that don't have too much of it but really don't care at all for a lot of that feel. Naturally this also varies according to the type of ski but in this case a good 113mm ski can have a reasonably wide range of application. A camber section underfoot eliminates this greasy feel and is more to my personal tastes.
This is almost exactly the way I'd put it, although I tend to use "vague," or "loose" to describe the feeling. And yep, to many, "loose" is approbative. Interestingly, I'm a lot lighter than Jim, and a lot less skier. So I don't think this is size or ability dependent, it's truly a personal preference.