A routine that satisfies the latter is an example of a non-preemptible routine. Interrupting means temporarily suspending the current processing flow and doing

A routine that satisfies the latter is an example of a non-preemptible routine. Interrupting means temporarily suspending the current processing flow and doing something else. Like, when a hardware interrupt has fired (data arrived on the network interface or the sound card, need to process right now...). If you want to know more - it's on Wikipedia for you :P (contrast preemptible with reentrant).