Tau (τ) leptons (aka tauons, tau particle) are one of the very small elementary particles. This means that they are believed to be so small that they can not be divided any more. Tau leptons can be thought of as very heavy electrons, as they are both leptons. This is because they have about 3,500 times as much mass as electrons, and about 17 times as much mass as muons. Since they only live for 2.9x10 seconds, they do not have a significant role in the regular world. However, they are very important in the decay of subatomic matter.