These states occur for the Event Scheduler thread, threads that are created to execute scheduled events, or threads that terminate the scheduler.
Clearing
The scheduler thread or a thread that was executing an event is terminating and is about to end.
Initialized
The scheduler thread or a thread that executes an event has been initialized.
Waiting for next activation
The scheduler has a nonempty event queue but the next activation is in the future.
Waiting for scheduler to stop
The thread issued SET GLOBAL event_scheduler=OFF and is waiting for the scheduler to stop.
Waiting on empty queue
The scheduler's event queue is empty and it is sleeping.