Scatters are symbols that start a payout or bonus feature no matter where on the reel they land.
Scatter symbols do not always multiply winnings as some players believe. In some games, two scatter symbols anywhere on the screen double your prize while three scatters quadruple winnings and four scatters payout nine times the winnings. The important point to remember is that scatters do not specify the type of prize they signify, only that a prize is generated whenever they appear on the screen. Scatters can also trigger a bonus game.
A bonus game is a free game that players acquire when or if they land a certain combination of scatter symbols. The bonus could be three specific bonus game symbols, three scatter symbols or any combination of three programmed into that machine. Bonus rounds are not played on the same machine.
The reel symbols may change or the value of the current symbols change. For example fruit symbols change into clown symbols for a bonus game. Players may also be taken to an entirely new slot machine.
Free spins are just that. A player hitting a set combination will receive a free spin. Often, the jackpot for combination increases during a free spin round. Free spins can also accumulate while the game continues.
A wild symbol in slots is similar to a wild card in poker. It can be substituted for other symbols to build winning combinations. Depending on the machine, wild symbols may or may not be substituted for bonus or scatter symbols.