Quantum Chromodynamics (QCD)
QCD, or Quantum Chromodynamics, is the theory in physics that describes the strong interaction. Developed in the early 1970s, QCD states that very short distances or, equivalently, at very high energies, quarks interact weakly and behave almost as free particles (property called asymptotic freedom). As quarks move apart, the force between them becomes stronger, effectively preventing the separation of individual quarks (phenomenon known as color confinement).