The point in a sample where the waveform reaches zero amplitude. When editing a loop, it is usual that both the beginning and end points of a loop are at a zero crossing. However, zero crossings are not important if the beginning and end points of the loop are at the same signal level and have about the same waveform slope. The harmonic content of the wave in the region around the loop point has much more effect on the quality of the loop than whether the loop point is at a zero-crossing.