Acronym for the phrase "tumble weed passes/ing/ed by". The asterisks are used to indicate the term between is actually happening. It is used exclusively online to convey the typist's boredom or mockery of the lack of activity in online contexts such as chat/game rooms and forums.
User1 posted 15/1/06: Hello does anybody talk here?
User2 posted 6/4/06: *twpb*
User1 posted 6/4/06: *cries from lonelines*