Quantum Chromodynamics (QCD) is the theory that describes the strong force, one of the four fundamental forces in nature. This force is responsible for holding together the protons and neutrons in atomic nuclei. QCD explains how quarks, the building blocks of protons and neutrons, interact through the exchange of particles called gluons. In QCD, quarks come in different types, known as "flavors," and carry a property called "color charge." This color charge is analogous to electric charge in electromagnetism, but it comes in three types: red, green, and blue. The strong force is incredibly powerful, but it operates over very short distances, making it essential for the stability of atomic nuclei.