The muon is a fundamental (indivisible) particle similar to the electron. It has the same electric charge but has a much greater mass than an electron. It is one of the charged leptons (fundamental particles that do not undergo strong interactions).

Muons are produced in collisions of cosmic particles with the atoms of the atmosphere and fly through our bodies on its way down. At sea level one can measure about one muon per minute within an area the size of a finger nail.

A muon is represented by the Greek letter mu (μ).