A 12 V LED is a high-powered LED. These are oftentimes utilized in applications for lighting. For example, car headlights might employ a 12 V LED.
12 V LEDs come in a wide variety of different sizes. One of the advantages of a 12 V LED is that it is compatible with battery-powered systems, such as those seen on automobiles, as well as other types of low voltage systems, for which 12 V is a common power supply.