What does PSK stand for?

Phase-Shift Keying

A communications method used by modems to encode data that relies on phase shifts in a carrier wave to represent digital informatioIn its sim-plest form, phase-shift keying allows the phase of the car-rier wave to be in either of two states: shifted 0 degrees or shifted 180 degrees, effectively reversing the phase of the wave. This straightforward phase-shift keying, however, is useful only when each phase can be measured against an unchanging reference value, so a more sophisticated tech-nique called differential phase-shift keying, or DPSK, is used in many modems.