A bounded surface set into a larger one. Also a small group convened to judge.
Latin pannus (a piece of cloth), via Old French panel (a small piece, a saddle-cloth); the sense of a bounded surface set into a larger one, and of a small group convened to judge, both descend from the idea of one bordered piece among many.
A bounded surface set into a larger one, or a small group convened to judge — both a defined space inside a bigger structure.