Plain English Meaning
A certification level used for big airplanes like airliners. To wear this label, the airplane has to be built and tested to the strictest safety rules the FAA has.
Full Definition
An FAA airworthiness certification category for large or turbine-powered aircraft, typically airliners and large business jets, certified under the most stringent design, performance, and structural standards in 14 CFR Part 25. Aircraft in this category must meet rigorous requirements for redundancy, performance after engine failure, structural integrity, and passenger safety.