A slot is a narrow opening in something, especially one used for receiving or admitting something, such as coins, letters or postcards. A slot can also refer to:
A small compartment or pocket in a garment for holding items such as keys or pens.
In computer science, a storage location or area that is assigned to a particular task or process. Whenever a query uses the allocated slots, they are immediately made available to other tasks. This ensures that all queries have the resources they need, and helps prevent resource starvation due to a single query taking too many slots.
This is especially important when using a shared database. When a large number of concurrent users are accessing the same database, a single query can take too many slots. When this happens, the system may be forced to preemptively borrow slots from other processes in order to avoid long delays. Preemptive borrowing is limited to a small fraction of the overall system capacity, so the effect on normal system performance is minimal.
Whether you play the classic machines that pay out only on a single line or modern machines with a host of bonus features, your success depends on luck as much as it does on strategy. So pick machines you enjoy. And be sure to read the rules of each machine before playing. This will improve your understanding of the game and tell you exactly how it works.