A subclass of the class Insecta comprising the winged insects and their secondarily wingless descendants. This subclass, including the great majority of insects, is usually divided into two infraclasses: Paleoptera, or ancient-winged insects (mayflies, dragonflies, and several extinct orders, most of which could not fold the wings over the body), and Neoptera, or folding-winged insects (the rest of the winged insects and some secondarily wingless lineages), which ancestrally folded the wings over the body by a particular articulatory mechanism.