Defining Terms

Mountain Goats

While listening to WYCE, the coolest radio station in Grand Rapids, I heard a pretty gnarly song. It was by the Mountain Goats, and I think the song was “Palmcorder Yajna”, the single off of their newest album, We Shall All Be Healed. The song has a pretty tubular style, and the lyrics are intriguing. Apparently, the whole album is about a group of tweakers the songwriter knew. But what is a tweaker? I have done some minimal searching on the web, and cannot find anything that might fit. Is this some kind of California slang or something that I don’t know about?