What does 'on' or 'off' the bridle mean?

Question

I've tried to get my head round this expression, and tried to see the difference in running when the commentator says a horse is on or off the bridle, but for the life of me, I can't figure out what's going on. Can anybody please enlighten me (in words of one syllable to the non-rider, but avid race follower, please)?

Answer 1

it means(aint 100% though) its on the bridle when the jockey is motionless on him and off the bridle when the jockey as to get to work

Answer 2

When a horse is off the bridle, it means he spit the bit and has quit pulling or driving forward.  So, obviously, you want a racehorse to be on the bridle, pulling, galloping on, or "on the bit."  Hope that was clear!