A North American telephony standard for converting analog voice into a digital data stream using pulse code modulation (PCM). The "pulse code" in PCM comes from the telephone company's method of sending a pulse or no pulse down the line.
Mu-Law signals typically ride on a single 64 Kbps DS0 channel in a T1 line. Mu-Law uses a companding technique that provides more quantization steps at lower amplitude (volume) than at higher amplitude. North America and Japan use mu-Law, while Europe uses A-Law. Mu-Law comes from µ-Law, which uses the Greek letter µ, pronounced "myoo." See PCM