A slot is a narrow opening in a machine or container, for example a hole that you put coins in to make a machine work. He dropped a coin into the slot and dialled the number. If you slot something into something else, or if it slots into it, you put it into a space where it fits. He was slotting a CD into a CD player.
CHANCE ONLY determines the outcome of any game, there is no play method or pattern that effects whether a game is winning or losing. Also, because outcomes are CHANCE ONLY, machines do not adjust to a string of winning or losing games causing them to be "due" for a win/loss.