A programmable power supply is a power source whose output voltage, output current, output power, and other electrical output characteristics can be configured or programmed at a very fine-grained level.
However, despite their sophisticated front panel controls, knobs, displays, and powerful user interface, they're not mere adjustable power supplies but far more than that. Their most unique aspect is that their power output behavior can be programmatically controlled in real-time using an external computer, as shown below.