What is a "sun dog"?

Mentioned in a Rush song, Chain Lightning- "Sun dogs fire on the horizon..." Peart was fascinated by atmospheric phenomena.

I wish the picture was of an actual Sundog, although I believe they are quite rare to see.

SOS, We see sun dogs from time to time here on the Canadian Prairies. They are very cool to look at.

SOS, you have to be at the right place st the right time, but they are not rare. I see them here in the Mojave Desert.

I have never seen one. Sounds really cool!