A slot is a narrow opening, especially one in a machine or container. A slot in a schedule or scheme is a time for an activity to take place. He dropped the coin into the slot and dialed. If he slots something into something, he puts it in its proper place. He is not a very good copy editor, but he has a lot of time to slot work into his schedule.
In a casino or other gambling establishment, the humming of many machines is accompanied by beeps and flashing lights. Well-dressed men and women walk around pushing buttons and pulling levers, watching cherries and sevens spin on liquid crystal displays. If they hit the right combination, they win a prize. Each machine has a pay table that lists the number of credits the player will receive if the symbols listed line up on a winning payline. Some machines use wild symbols, which can stand in for multiple other symbols to complete a winning line.
In Web development, a slot is a dynamic placeholder that either waits for content (passive) or calls out for it (active). A slot can reference a repository item with a bunch of content in it (content repository), or it can point to a renderer (which specifies how the slot’s content should be displayed). A slot’s contents are controlled by its parent scope and by scenarios using an add to slot action or a targeter to specify where to place the content in the slot.