DC offset
When an audio waveform swings around a constant shift above or below zero instead of around zero itself.
Audio should average out to zero. A cheap ADC, a tired sound card or an asymmetric distortion effect can add a direct-current component that shifts the whole wave. You can't hear it as such — 0 Hz isn't a pitch — but it causes trouble elsewhere.
The offset eats headroom on one side, so the wave clips sooner going up than going down. Cut a region where the wave doesn't cross zero and you get a click, because the level jumps from the offset straight to silence. The cure is a high-pass filter at a few hertz, and most DAWs have a button for it. A waveform that sits visibly above the centre line is the giveaway.