When I first started smoking more than 20 years ago "bowl" and "pipe" were usually used to describe different things. A "pipe" was, well.. a pipe. Duh! The "bowl", however, is the actual area of the pipe where you put the weed. Think about it, it is shaped like a bowl. So, a pipe ,a bubbler, and a bong all have "bowls". Over the years, however, people just started using "bowl" as a generic word for pipe. But back then, if somebody said the just got a new bowl you'd wonder what they were talking about.