"Chalk - When a horse is the favorite -- or has the most money bet on it -- that horse is termed the "chalk." Interestingly, this term comes from the pre-computer era of the bookie. When a bookie recorded bets on a blackboard, the odds would change over and over as more and more people bet on the favorite. The horse became known as the "chalk" because the horse's name would disappear in chalk dust as the bookie constantly erased and lowered the horse's odds."
