Leptons are a family of six fundamental particles that, unlike quarks, are never bound together by the strong force and can exist entirely on their own. The most familiar lepton is the electron, joined by two heavier versions of itself, the muon and the tau, plus a neutrino partner for each.
Charged leptons like the electron interact through electromagnetism and the weak force, while neutrinos, being electrically neutral, interact so weakly with everything else that trillions pass through your body every second without leaving a trace.
Leptons are classified as fermions, meaning no two identical leptons can ever occupy the same quantum state. Together with quarks, they make up all of the matter described by the Standard Model. Astrinova’s particle physics guide covers where leptons fit into the bigger picture.