The tau (t), also called the tau lepton, tau particle or tauon, is an elementary particle similar to the electron, with negative electric charge and a . Together with the electron, the muon, and the three neutrinos, it is classified as a lepton. Like all elementary particles, the tau has a corresponding antiparticle of opposite charge but equal mass and spin, which in the tau's case is the antitau (also called the positive tau). Tau particles are denoted by and the antitau by .