Bum shadow 

The area beneath the bottom cheeks left white by a tanning machine due to the posture adopted by the sitter.

Look at that micro-bikini over there!" "Yes. Its so small you can see the bum shadow.

Bum shadow by aureliozen June 27, 2010

Shadow Bum 

A homeless person that lurks in the shadows, normally in alleyways, and appears seemingly out of nowhere to ask for change or other items.

Shadow Bums can appear day or night, but mainly strike when you think the area is free of homeless.

"I checked around for bums and everything. I thought the area was clear, but then out popped a shadow bum from behind the building and he asked me for a cigarette!"

Shadow Bum by wayoutofplace April 24, 2008