What is this?

Definitely fretless with flats... a lot like Jaco Pastorius' tone... which was a Fender Jazz (fretless - took the frets out of a fretted 60s bass, filled the whole thing in with wood filler, and then used epoxy for protection, although he used round Rotosound 40-85) through two of these into Hartke cabs with aluminum-cone speakers.

Jeff