A theoretical new state of matter. Quarks and gluons are components of atoms. When you heat certain atoms to around 4 trillion degrees Celsius, the atoms stop behaving as atoms and start behaving as something completely different.

A quark-gluon plasma behaves as a near-ideal Fermi liquid.

In normal matter, quarks are confined, in a Quark Gluon plasma, the quarks are not confined (read more on deconfinement).

At such temperatures, you would think that the quark gluon plasma would behave as free roaming objects, as people normally experience a gas, but it behaves more like a liquid instead.

More experiments are required to explore the nature of these subatomic particles.