Quantum chromodynamics (QCD) is a fundamental theory in particle physics that describes the strong interaction, one of the four fundamental forces of nature. It explains how quarks and gluons, the building blocks of protons and neutrons, interact with each other. QCD is essential for understanding the behavior of matter at the smallest scales. In QCD, quarks carry a property called "color charge," which comes in three types: red, green, and blue. Gluons are the force carriers that mediate the strong force between quarks, similar to how photons mediate the electromagnetic force. This theory is crucial for explaining phenomena in high-energy physics and the structure of atomic nuclei.