What does the abbreviation "PSK" mean?

PSK stands for Phase Shift Keying. It is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave). This technique is widely used in popular amateur digital modes. The most notable example is PSK31, which is a highly efficient mode used for live, keyboard-to-keyboard text chat on the HF bands, especially under weak-signal conditions. Distractors like 'Pulse,' 'Packet,' or 'Phased Slide' are simply incorrect variations designed to test if you know the exact technical term for shifting the radio wave's phase.