The Meeting Request Summary is a simple Total count of all the requests made for the event - plus a breakdown of their current status:

Pending - pure requests that have never been scheduled, nor approved/declined by the targets.

Approved - accepted as a request - either by the moderator or target - but not currently scheduled into a meeting.  Note - this can include a request that a moderator put into a meeting, and then took out again, but remains as "approved"

Confirmed - scheduled into a confirmed meeting

Declined - declined or deleted - no longer active.