Wild slot machines are one of the most common bonus you will find in slot gaming. The game will have a special symbol, usually something related to the games theme, that is designated as being wild. When the symbol lands on a pay-line it will be considered as the symbol of whichever normal symbol would give you the highest payout. The symbol will also increase the amount you will win.
The more wild symbols you have on a line the bigger your prize amount will be multiplied. On some wild slot machine you will need to have an entire pay line of the wild card symbol to win the jackpot.