Plain English Meaning
The official rules that say what an airplane must be built and equipped to do before it is allowed to fly. If an airplane meets these rules, it is approved as safe to operate within the limits set during its certification.
Full Definition
The federal regulations that establish the minimum design, construction, performance, and equipment requirements an aircraft must meet to be certified as safe for flight. For civil airplanes, these are codified primarily in Title 14 of the Code of Federal Regulations (14 CFR), with different parts covering different categories of aircraft (for example, Part 23 for normal category airplanes and Part 25 for transport category airplanes).
Context Anchor
In the intentional spins , this term matters because not every airplane is approved for or intentional spins.