Phase

One swing of a pulse away from the baseline and back. A pulse that goes one way only has a single phase and is called monophasic, or unipolar; a pulse that goes one way and then the other has two phases and is called biphasic, or bipolar. The word matters because it is where a pulse count and a frequency part company: counting phases gives twice the number that counting complete pulses does, so a specification that reads double a measured frequency is often counting phases. Clinical electrotherapy keeps the two apart by naming them separately, where phase duration is the time the current flows in one direction and back and pulse duration is the time it flows in both. This is the pulse sense of the word and not the phase angle of a sine wave, which is a different quantity that shares the name. See Bipolar Pulse and Pulses Per Second (pps).