MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
These states occur for the Event Scheduler thread, threads that are created to execute scheduled events, or threads that terminate the scheduler.
The scheduler thread or a thread that was executing an event is terminating and is about to end.
The scheduler thread or a thread that executes an event has been initialized.
The scheduler has a nonempty event queue but the next activation is in the future.
The thread issued SET GLOBAL
event_scheduler=OFF and is waiting for the
scheduler to stop.
The scheduler's event queue is empty and it is sleeping.