Plain-language answer: PSK31 is a narrowband keyboard-to-keyboard digital mode using phase-shift keying at roughly 31 baud.
Why operators care
Its narrow signal can work well at modest power, but overdriven audio creates wide unwanted products that interfere with neighboring conversations.
How to use it well
Use an unprocessed linear transmit path, set audio for no ALC or only the manufacturer-approved indication, and center the signal in the software passband.
The common mistake
Increasing audio drive until the waterfall trace becomes brighter and wider.
Operating boundary
Predictions, reports, schedules, and mode descriptions guide a decision; they do not override current regulations, equipment limits, exact station conditions, or what the operator verifies on air.
