Process State where the Process is actively being executed by the Central Processing Unit (CPU).
- Only one process per CPU core can be in this state at a time
- Executes in either User Mode or Kernel Mode (entered via System Call)
- Transitions to Ready (Waiting) if preempted (see Preemptive Multitasking) or if it yields
- Transitions to Blocked if it requests I/O or blocks on a resource
- Transitions to Terminated when execution ends