A Rain Dog is a dog caught in the rain, with its whole trail washed away by the water so he can't get back home. A stranded dog, who wants nothing better than to get home.
People who live outdoors, people who sleep in doorways, loners knit together by some corporeal way of sharing pain and discomfort.
A term coined by Tom Waits on his album named Rain Dogs
Inside a broken clock
Splashing the wine with all the rain dogs
Taxi, we’d rather walk
Huddle a doorway with the rain dogs
For I am a rain dog too
(from Tom Waits' Rain Dogs)