According to a distinction that originates with Aristotle himself, his writings are divisible into two groups: the "exoteric" and the "esoteric". Most scholars have understood this as a distinction between works Aristotle intended for the public (exoteric), and the more technical works intended for use within the Lyceum course / school (esoteric). Modern scholars commonly assume these latter to be Aristotle's own (unpolished) lecture notes (or in some cases possible notes by his students). ... Another common assumption is that none of the exoteric works is extant – that all of Aristotle's extant writings are of the esoteric kind.

Wikipedia on Aristotle