QCD stands for Quantum Chromodynamics, which is a branch of theoretical physics that explains the behavior of subatomic particles, especially quarks and gluons, through the strong nuclear force. Some synonyms for QCD include "the theory of strong interactions," "chromodynamics," and "the strong force theory." Additionally, QCD is often used interchangeably with the term "gauge theory" since it relies on the gauge principle of invariance to describe the behavior of quarks and gluons. Some other related terms include "asymptotic freedom," "confinement," and "hadronization," which describe the behavior of quarks and gluons in different energy regimes. Ultimately, QCD is an essential part of understanding the standard model of particle physics and the behavior of the universe at a fundamental level.