quark matter

The term quark matter (abbreviated QM; aka QCD matter, "QCD" standing for quantum chromodynamics, the theory that includes quarks) is matter not made up of protons and neutrons but of quarks, the particles that make up protons and neutrons. Quark matter is a general term as there are a number of theories of such types of matter that could exist, among them:

• quark-gluon plasma (QGP).
• strange matter aka strange quark matter, consisting of strange quarks, one of the six quark flavors (flavor being a term used for the types of quarks).

QGP is presumed to have filled the early universe for an interval of time. Possibly some or all neutron stars include a core of quark matter (quark condensate), but I'm not sure of the type of quark matter favored by theory. The term quark star has been used to refer to such neutron stars. A more exotic theory is the existence of strange stars, stars of strange matter formed during the early universe when quarks were just combining to form protons and neutrons.