Insulator
Also called Nonconductor
An insulator is a material whose charge carriers cannot move easily, so charge stays where it is placed rather than spreading over the surface. Glass, rubber, plastic and dry air are insulators; they polarize in a field but do not conduct.
Same CED sentence as the conductor, other half: insulators are made from electrically nonconducting materials in which charge carriers cannot move easily.
The consequence is local charge. Put charge on one spot of an insulator and it stays on that spot, so one object can carry different amounts of charge in different places. That is why rubbing a balloon on hair charges the patch you rubbed, and why a charged insulator holds its charge long enough to demonstrate anything at all. On a conductor the same charge would spread over the whole surface within an instant.
An insulator still responds to a field. Its electrons cannot leave their molecules but they can shift within them, so the material polarizes: positive and negative charge separate slightly and the material sets up a small field of its own opposing the applied one. Electric permittivity is the measure of how readily that happens, and it is the reason a charged rod attracts neutral scraps of paper.
AP Physics 2 keeps the interior qualitative. The Topic 10.3 boundary statement says students will only be expected to perform qualitative analysis of electric fields within insulators.
An insulator placed between capacitor plates gets a job title rather than a new identity: there it is called a dielectric.