Color confinement is a fundamental principle in quantum chromodynamics (QCD), the theory that describes the strong force in particle physics. It states that quarks, the building blocks of protons and neutrons, cannot exist in isolation. Instead, they are always found in groups, such as in hadrons, which are composite particles made of quarks held together by the strong force. This phenomenon occurs because quarks carry a property called "color charge," similar to electric charge but with three types: red, green, and blue. When quarks combine, they must form a color-neutral state, meaning the colors must cancel out. This is why we never observe free quarks; they are always confined within particles like protons and neutrons.