Pterygota is a subclass of insects that includes the winged insects. It also includes insect orders that are secondarily wingless. That means insect groups whose ancestors once had wings but that have lost them later in evolution.
The Pterygota today includes almost all insects. That is because flying led to a great radiation of insect types. The groups without flight are in the Apterygota.
In the Pterygota, are the Palaeoptera and the Neoptera. The Palaeoptera is paraphyletic, and its classification is being discussed. Likewise the Exopterygota. There are no agreed alternatives at present, so the taxonomy is left in its traditional form.
The Endopterygota is made up of all the insects which have complete metamorphosis. It is agreed to be a good monophyletic clade, even though some of the details may need to be adjusted.