The indentation on one's ass that occurs from sitting unclothed on a patterned surface-namely pavement-for an extended period of time. The said indentation usually resembles a sort of mosaic that might be found hung in an ancient Roman villa; next to a frescoe, perhaps? Most often occurs whilst smoking nude in a jacuzzi of suds. Inappropriate in every circumstance.
"Well, I've been sitting nude on this pavement too long and now I've got a bitchin' ass mosaic; look."