If you remember the old oscilloscope experiments you did in physics, you might remember a sine wave was half in the positive and half in the negative: the average position then, over a wavecycle, was zero. This is analagous to 'alternating current' (A.C.) and is the sort of voltage in mains electricity, at 50Hz (cycles per second). Battery electricity, on the other hand, is a flat voltage - called 'direct current' (D.C.), which would measure as a straight line on our oscilloscope (0 Hz).

Now, in digital sound-files, we can measure the component at 0Hz by measuring what the average sample value is, and how much this has 'drifted' from zero (look in the Statistics effect for a DC offset measure). Most sound files that have been recorded through analogue equipment should have little, if any, DC offset. However, sometimes (due to digital processes) we may end up with a sound that does have a considerable DC offset.

This can be a Bad Thing. Why? Well, playing sounds with high DC Offset for too long can harm speakers. Furthermore you're losing a certain amount of possible amplitude bandwidth.

As well, DC Offset can cause 'drift' in delay-line effects, especially the Comb Filter Bank.

There are none - it just goes ahead and removes that offset...