Originally Posted by slawecki
I think a "D" fare is a discounted business class. Although seats show, the fare does not, under usual searching. A Z fare also sometimes shows up. I think on some airlines (not sure about UA) that is a discounted first class fare. It also does not show up with the normal booking tools.
D is discounted business class, Z is deeply discounted business class. United.com should show a Z or D fare if all parameters of any available fare are met. Travelocity Fare Listings does not by default show anything but coach fares, I thin.