what is certified on a used car

It depends on the certified program as they all differ in inspection and coverage. Here is the link to the Caddy Certified Page http://www.cadillac.com/certified-pre-owned-vehicles/benefits.html

Want to save money? - get a 1 yr old Caddy with low mileage from a Caddy dealer. Besides possibly saving a considerable amount of money you will get a Certified Pre-owned warranty that goes 6 yr or 100k miles instead of the new car warranty that is 4 yr or 50k miles.