Vomit, or anything that looks or is related to vomit.
Eww, someone urched on the sidewalk.
A kind of underground culture developing or developed around east london. Can be linked with Indie and has a large musical community surrounding it. These include The Libertines, Babyshambles, The Rakes adn other such bands with hard hitting simple drums and scratchy messy guitar playing. Lyrics are usually centred around going out on the town or about city life in general but can also be deeper. The word may originate from the word urchin because if u look at people such as the libertines they could be described in some way as an urchin of the street.
The Rakes album Capture/Release sounds like a Metropolitan Tube Train travelling at full speed through the depths of the underground with the dead carcass of the urch scene underneath its rusted wheels.