What is Quantum Chromodynamics (QCD)?

References: Quantum Chromodynamics - Wikipedia https://en.wikipedia.org/wiki/Quantum_chromodynamics Strong CP (charge-parity) Problem - Wikipedia https://en.wikipedia.org/wiki/Strong_CP_problem Quark - Wikipedia https://en.wikipedia.org/wiki/Quark Origin of the Word “Quark” - ScienceFriday https://www.sciencefriday.com/articles/the-origin-of-the-word-quark/ Eightfold Way (Physics) - Wikipedia https://en.wikipedia.org/wiki/Eightfold_way_(physics) Color Charge - Wikipedia https://en.wikipedia.org/wiki/Color_charge Non-Abelian Gauge Theory - Wikipedia https://en.wikipedia.org/wiki/Non-abelian_gauge_theory Lagrangian Function - Britannica https://www.britannica.com/science/Lagrangian-function Yang-Mills Theory - Wikipedia https://en.wikipedia.org/wiki/Yang%E2%80%93Mills_theory Special Unitary Triplet - Wikipedia https://en.wikipedia.org/wiki/Special_unitary_group#The_group_SU(3) Asymptotic Freedom - Wikipedia https://en.wikipedia.org/wiki/Asymptotic_freedom Color Confinement - Wikipedia https://en.wikipedia.org/wiki/Color_confinement Direct Photon Production - Wikipedia https://en.wikipedia.org/wiki/Direct_photons Jet (Physics) and Hadronization - Wikipedia https://en.wikipedia.org/wiki/Jet_(particle_physics) Peccei-Quinn Theory - Wikipedia https://en.wikipedia.org/wiki/Peccei%E2%80%93Quinn_theory Axion - Wikipedia https://en.wikipedia.org/wiki/Axion