Sign up bet or no deposit bet: these free bets are usually given to you when you sign up to a sportsbook. They're usually quite small (aroundR$25), but you don't have to make a deposit, so it's a great way to have a flutter without spending any money.
Horse race betting is pari-mutuel rather than traditional sports betting. This is why the activity has always been regarded as operationally separate from house-banked sports betting. Horse race betting is not considered gambling in many jurisdictions, which is treated similarly to a lottery.