Interrupt
An 
Interrupt is a term that is used to describe an interruption of normal code execution needing immediate attention.  An interrupt can be triggered via a piece of hardware (input pin), or it can exist in software such as a timer interrupt.  An interrupt allows the software code to jump into a special routine that can quickly address a function that might otherwise not commonly occur or doesn't happen with any regularity.  An example of a use of an interrupt is when a robot is handling a button input.  Using an interrupt for a button trigger can be more efficient than polling the input pin and wasting valuable processing time.  
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