Acronym for Maximum Output Level. This is a spec often associated with analog tape machines and is generally taken to mean the output signal level that results in 3% harmonic distortion and low frequencies or 3% intermodulation distortion at high frequencies. The idea is that any higher signal level will result in rapidly increasing distortion. It’s not intended to be an absolute level in a conventional electronics sense, but more a function of a device system – like a tape machine with a particular type of tape. Often time MOL is plotted against frequency so an engineer or technician can address how a machine responds across the frequency spectrum.