Phase

From AudioLexic

Expressed in degrees, it is used to describe an offset in a waveform’s cycle. A complete cycle is 360 degrees; therefore, waveforms at 0 degrees or multiples of 360 degrees offset are said to be in phase, while any other number would result in waves that are out of phase.

Many mixing consoles provide a switch to invert the phase of a signal by 180 degrees. This is often useful in multiple microphone recording, when signals arrive at two or more mics out of phase, causing frequency cancellation.