Coin

Golden Coins (sometimes known as Coins) are coins that are found commonly throughout the Mushroom Kingdom. Most of the time, when Mario finds one of those, it will give you energy. They are also counted up at the end of the level in a number of games, contributing to a high score or some sort of bonus. In various games, some are found in lines or groups on the floor while others are found when defeating enemies, opening boxes, or other events.

In the Paper Mario series of RPGs, coins are actually saved up and used for purchasing items, particularly badges. In Mario Party, coins are gained through winning mini games and are used to purchase stars.

Other Types of Coins
Dragon coins are coins that are usually found five in each level in Super Mario World. If you get all five coins, then you would get a 1-up.

Star Coins are coins that are found in New Super Mario Bors.(three per level). Five of these coins will unlock a mushroom hous and 20 will allow the player to by a new skin from the blue mushroom house

Red Coins are red-colored coins found in several games that are found in collections of 8 and a reward is received when all eight are found.

Blue Coins are blue-colored coins that are worth 5 golden coins when found.