BPOS is the player's best position. Each position they have a star rating, the better the rating the better they play. The way admins have made it sound it is no more or less important than major attributes at a position(passing for QB's, catching for WR's, etc.)

TwoPint wrote: Note also that it is what the game currently sees as the best position for your player and may not be the position where the player should be played long-term.

Exactly, I had a Running back with 4 talent and the coaches didnt say he could play linebacker, but I played him at that position anyway and now I have a great linebacker.