Term used to describe the result of an amplifier running into power supply limitation. The maximum output voltage that any amplifier can produce is limited by its power supply. Attempting to output a voltage (or current) level that exceeds the power supply results in a flattoping effect on the signal, making it look cut off or "clipped." A clipped waveform exhibits extreme harmonic distortion, dominated by large amplitude odd-ordered harmonics making it sound harsh or dissonant.
Hard clipping is the term used to describe extreme clipping of a signal, producing highly visible flattoped waveforms as viewed on an oscilloscope;
soft clipping refers to moderate clipping that results in waveforms having softly-rounded edges, as opposed to the sharp edges of hard clipping. For how-to-avoid see the RaneNote
Setting Sound System Level Controls.