Quantum Chromodynamics (QCD) is a theory in particle physics that explains how the fundamental particles called quarks and gluons interact. These particles are the building blocks of protons and neutrons, which make up atomic nuclei. QCD describes the strong force, one of the four fundamental forces of nature, that holds these particles together. In QCD, quarks carry a property known as "color charge," which is similar to electric charge but comes in three types: red, green, and blue. Gluons are the force carriers that mediate the interactions between quarks, ensuring that they remain bound within particles like protons and neutrons. This complex interplay is essential for understanding the structure of matter in the universe.