A down quark is a fundamental particle that is one of the building blocks of matter. It is a type of quark, which is a subatomic particle that combines with up quarks to form protons and neutrons. Down quarks have a negative electric charge of -1/3, which contributes to the overall charge of these particles. Down quarks are part of the Standard Model of particle physics, which describes the fundamental forces and particles in the universe. They are classified as fermions and belong to a group called leptons and baryons. Understanding down quarks helps scientists explore the structure of matter and the forces that govern it.