Star Coins are items in the Mario series. There are three Star Coins in every level and they can be used to unlock levels, item shops, tips, and other things depending on the game. They are usually hidden in hard to reach areas that require precision platforming.
New Super Mario Bros.: Superstar Adventure
Star Coins appear in every level of New Super Mario Bros.: Superstar Adventure. They can be used to buy new mini-games at Peach's Castle.
In this game, star coins are known as star medals, & 3 can be collected in each of the 48 main courses (144 in total).