Parton - Definition and Overview

In particle physics, the parton was a hypothetical fundamental particle considered, in the 'parton model' of strong interactions, to be a constituent of the hadron. In the 1970s, quantum chromodynamics showed that hadrons are composed of quarks, but the parton model is still used to explain some aspects of short-distance interactions.

The preon is yet another hypothetical fundamental particle in quark compositeness theories.