The Event Viewer filter displays how many events there are at each severity and status. The left side of the filter displays event severity, such as Fatal or Severe; the right side of the filter displays the status of the event, such as Acknowledged or Closed.
You can use the filter to control the events displayed in the Event Viewer window. To filter out events of a specific severity or status, click the button for the status or severity you want to filter out. To redisplay these events, click the button again. The default is to have all severities and statuses displayed.