In the context of high-energy hadron collisions, quarks and gluons are collectively called partons. The jets emerging from the collisions originally consist of partons, which quickly combine to form hadrons, a process called hadronization. Only the resulting hadrons can be directly observed. The hot, dense medium produced in the collisions is also composed of partons; it is known as a quark–gluon plasma (QGP). In this realm, the laws of physics that apply are those of quantum chromodynamics (QCD).