A free spin is essentially an offer that a casino gives to its players to spin the reels free of charge and have the opportunity to win real cash. The free spins may be given to both new and current customers, and it's one way to reward and encourage them to continue betting.
Macau is a former Portuguese colony, and an administrative region of China, which depends on gambling tourism. Casinos and shopping malls characterize the region, and today it rakes in more revenue than popular casino hubs like Las Vegas. It is the only place in China where gambling is legal, making it a top destination.