An EVENT happens when any counter is changing its status to (yellow) WARNING alert level or to (red) CRITICAL alert level. And this EVENT is over when the counter becomes stable. The EVENT table gives an overall view of all such EVENTS that have happened on each server.
An alert (WARNING or CRITICAL) can be closed (and re-opened) for a specific server from both the EVENTS overview page as well as the Monitors page.
Closing an event is temporarily disabling an EVENT meaning, disabling alerting with the yellow/red on the monitors page or sending notifications until it becomes stable, and then goes to the CRITICAL/WARNING (yellow/red) state.
EVENTS can be closed from both the Monitors page (by clicking on the red/yellow alert) and the EVENTS page. Opening the closed EVENTS can be done from the EVENTS page. Closing ALL EVENTS for a certain server from the Monitors page is possible.