X-plan is a Ford program originally designed as a marketing benefit for "partners" -- companies that Ford did a lot of business with. Ford has an "A plan" for employee discounts, a "Z plan" for retirees, and a "D plan" for dealership employees. Then there's the "X plan".
It's become a pretty broad category by now. Some clubs, like SVTOA or the EAA, have an X-plan benefit as part of their membership. You normally need to have been a member of whatever organization for 60 days to qualify. Also, Ford employees get a certain number of X-plan PINs per year that they can give away as part of the "Friends and Neighbors" category of the X-plan. Finally, if you directly own at least 100 shares of Ford stock for at least six months, you can get an X-plan PIN.
X-plan pricing works out to about a few hundred dollars over invoice. (99.6% of invoice, plus a max $100 doc fee, plus a $275 admin fee; fuel and advertising fees are added depending on your region. The dealer can print an invoice showing the exact X-plan price for you.)