This light comes on briefly when the ignition key is turned on, but the engine is not running, as a check to show it is working.

It should go out once the engine is running. If it stays on, or comes on while driving, there could be a problem with the charging system or it could indicate that there are problems with a generator drive belt, or that there is an electrical problem. Have it checked right away. If the vehicle must be driven a short distance with the light on, to turn off the accessories, such as the radio and air conditioner.