An interrupt is a signal to the computer to stop what it is doing and do something else. These are used extensively by the operating system, but an application can use them as well. If you have a GPIO input that needs to be responded to, you could poll the GPIO pin in a loop waiting for it to change, but this can be unreliable for very brief state changes. It is also wasteful of the CPU. The better way is to assign an interrupt that will be activated when the GPIO pin changes state.
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