Chiral symmetry breaking is a phenomenon in particle physics where a system that is symmetric under certain transformations loses that symmetry. In simple terms, it means that the behavior of particles changes in a way that distinguishes between left-handed and right-handed versions of particles, known as chirality. This breaking is crucial for understanding the mass of certain particles, particularly in the context of the Standard Model of particle physics. This concept is particularly important in the study of quantum chromodynamics (QCD), the theory that describes the strong interaction between quarks and gluons. When chiral symmetry is broken, it leads to the formation of pions as composite particles, which are essential in explaining how strong forces operate within atomic nuclei.