seeking a GM certified used wagon.what does certified mean with GM?

Certified Pre-Owned Vehicles from Chevy, Buick and GMC are a smarter way to buy your next used vehicle, because they provide you with the confidence of new and the affordability of used. Only select cars, trucks and SUVs from Chevy, Buick, GMC, Pontiac and Saturn that meet our strict age, mileage and condition requirements can become Certified. Many don't make the cut because they can't meet the standards we've created. Each Certified Pre- Owned Vehicle from Chevy, Buick or GMC must undergo a rigorous 172-Point Inspection and an extensive mechanical and appearance reconditioning process. Once Certified, it receives our new, exclusive 2-Year/30,000-Mile1 Standard Certified Pre-Owned Maintenance Plan, and is then backed by both a 12-Month/12,000-Mile2 Bumper-to-Bumper Limited Warranty and a 5- Year/100,000-Mile3 Powertrain Limited Warranty.

okay yet what does limilted power train mean? what does 3powertrain limited warranty mean? I do not mean to harrass. I just am seeking to have this matter clear in my mind. A dealer desired to sell me a warranty from some official sounding company.I preferred the GM. The vehicle did not qualify apparently.