Chapter 10 Install and System Administration for FortiOS 5.0 : Using the web-based manager : Dashboard : Top Sessions widget
  
Top Sessions widget
The Top Sessions widget polls the FortiGate unit for session information for IPv4 or IPv6 addresses, or both. Rebooting the FortiGate unit will reset the Top Session statistics to zero.
When you select Details to view the current sessions list, a list of all sessions currently processed by the FortiGate unit.
Detailed information is available in System > Monitor > Sessions. Use the following table to modify the default settings of the Top Sessions widget.