Quark-gluon plasma is a state of matter that is believed to have existed in the early universe shortly after the Big Bang, before the formation of protons and neutrons. In this state, quarks and gluons, which are the fundamental building blocks of protons and neutrons, are not confined within individual particles but move freely as a collective. Researchers study quark-gluon plasma in high-energy nuclear collisions, such as those at the Large Hadron Collider, to understand the properties of this unique form of matter and the conditions of the early universe. By studying the behavior of quarks and gluons in this extreme state, scientists can gain insights into the fundamental forces of nature and the evolution of the universe.