There seems to be two definitions of boline floating around. 1. A boline is a curved knife, with a blade that looks something like a crescent moon. A traditional boline would have a white handle, but it's not crucial. A boline would be used to harvest herbs, much like a sickle.
2. Any ritual knife (curved or not) that is used for all ritual cutting tasks, unlike an athame. It would still have a white handle and could be used to scribe candles, trim herbs, cut paper, or any other task.
Blessed Be!
http://paganwiccan.about.com/