Volvo: Bulb Failure Position Light., bulb failure, volvo s 80

Question
I have a 2001 Volvo S-80.  I have the message Bulb Failure Position Light, but it appears all of the bulbs are working fine.  What is a position light?

Answer
Tom,
Position light is a parking light. There are two on each side rear, look carefully and find the bulb that is out and replace it. At night would be best. I have looked at the rear light in daylight and find it difficult to identify a burnt out light without covering the unit to look.