A LED driver is an electrical device that regulates the power to an LED or string(s) of LEDs. What makes a driver different from conventional power supplies, is that an LED driver responds to the ever-changing needs of the LED, or circuit of LEDs, by supplying a constant amount of power to the LED, as its electrical properties change with temperature.
Think of an LED driver as ‘Cruise Control’ (like in a car) for the LED, and the temperature changes of the LED are the hills and valleys it is ‘driving’ over. The power level (or ‘Speed’) of the LED is maintained constant by the driver as the electrical properties change (amount of ‘gas’ or power needed) throughout the temperature increases and decreases (or ‘hills and valleys’) seen by the LED(s). Without the proper driver, the LED may become too hot (driving too fast) and become unstable (out of control), causing poor performance (engine problems) or complete failure (crash!)