A narrow notch or opening, as in a keyway, in a door, or in a machine. Also called slit, channel, vent, or aperture. To fit into or assign to a slot; place in a position: He slid the new filter into the slot. (From American Heritage Dictionary of the English Language, Fifth Edition.)
A slot is a specific slot in a machine where you insert coins or other tokens to play the game. The slots on a slot machine are arranged so that they will line up with the symbols on the paytable, which shows what each symbol is worth.
There are two types of slot: mechanical slots and video slots. Mechanical slots have physical reels that spin and sometimes use levers to initiate play, while video slots use microchips to generate combinations and determine outcomes. The odds of winning are determined by the weighting of the symbols on each reel, which is why it is possible to see JACKPOT on two consecutive reels, but not on the third.
A slot can be a theme or a period of history that draws in people in search of their fortunes, like the California Gold Rush or Klondike Gold Rush in the US. Depending on the theme, slot games can have different types of symbols and paylines. They usually include the classical symboles from a card deck like A(ce), K(ing), Q(ueen) and J(oker), sometimes the 10, and themed symbols fitting the theme of your slot.