What does the abbreviation "PSK" mean?

PSK stands for Phase Shift Keying. It is a highly efficient digital modulation method that transmits data by changing, or modulating, the phase of a continuous reference carrier wave. This technique is the foundation for popular amateur digital modes like PSK31, which is favored for its incredibly narrow bandwidth and excellent performance even in poor signal-to-noise conditions. Distractors like "Pulse Shift Keying" or "Packet Sampled Keying" use plausible-sounding technical words to trick you, but they do not accurately describe this phase-based modulation technique.