Tau is a lepton just like electron and Muon. It is considered to be a point-like particle since it doesn’t have internal structure, as far as it’s known. Taus have a mass of 1777 MeV which is about 3500 times more than an electron. They are also twice as heavy as protons. Being so massive meant that they were not easily discoverable because energies of 1.7 GeV or greater were needed. Finally in experiments that ran in 1974-7, some 40 years after discovery of muon, taus were discovered by a group of experimentalists at SLAC.

Taus are able to decay into hadrons via weak interaction, and this makes them unique in the leptonic world. Taus are very unstable, thus they have a very short lifetime of 3 ⋅ 10⁻¹³s

As a member of the 3rd leptonic group taus have an anti-particle partner anti-tau, and also two neutrinos, a tau Neutrino and anti-tau neutrino.