I checked everywhere for what "reserved" meant for a status on a sales order and couldn't find anything. When running the scheduled event ticket detail report, this shows the number of people attending, number of tickets reserved and the number of tickets still available.
The number of tickets reserved on the Scheduled Ticket Event Detail Report means these tickets were entered into Advance Sales and were marked as Pay on Arrival.
Click the Order # hyperlink
This should open in Advance Sales
On the Payments tab, enter the payment, click Complete