BFM stands for BirdieFire metric. It works just like a standard handicap system where + handicaps usually represent the best players. BFM is a combination of skills within the game that aid or are detrimental to scoring potential. It is a combination of missed fairway percentage, strokes in, scrambling, and strokes gained putting. Within these four categories things like penalty shots etc. are all factored in.
Here is a sample report with all categories explained