The Muon Mass constant represents the mass of muon expressed in kilograms (kg): 1.883531475E-28 kg.
A muon is an elementary particle classified as a lepton which has properties similar to an electron: it has spin of -1/2 and charge of -1. The muon however has significantly more mass than an electron.
This constant is specified with a standard uncertainty (standard deviation) of: 0.000 000 096 E-28 kg