What is Tic-Tac?

Tic –Tac is a mix of hand signals and cockney rhyming slang used to communicate racing odds between staff (bookmakers) at arenas. They use the method to ensure their odds are different from competitors an advantage the punters could otherwise exploit. In particular, if a very large bet is placed with one bookmaker, this may be signalled to the others as a way of lowering the price on all the boards.

It is less commonly found at race tracks now but some of the slang terms are still used and pundits still will use the hand signals.