Short-term scheduling
Short-term scheduler is invoked whenever an event occurs that may lead to the interruption of the current process or that may warrant the preemption of the current process in favor of another.
Clock-interrupts, IO interrupts, OS calls, signals, real-time system policies are some such events.
The main objective of short-term scheduling is to allocate processor time in such a way as to optimize one or more aspects of system behavior.