Marketing-speak for a chronic oil leak on your automobile - generally one that takes more effort to fix than the car is worth. Comes standard on most General Motors products since the early 60s, as well as Saab 900 series.
Click: Dude have you seen that grease spot on your inner fender?
Clack: Oh don't worry about it, that's just active undercarriage rust protection. Paid extra for it. I think.