Hi Ron,
That designation is in referenced to the line above:
"Maximum Throughput (Mixed RFC2544)* Open/Encrypted"
Open =- No Encryption (5 Gbps for Small config; 10.8 Gbps for the Medium and Large config)
Encrypted - Served over IPsec tunneling between APs and Appliance (1.8 Gbps for Small; 5 Gbps for Medium and Large)
Note: The throughput of the VM depends on the asssigned resources, such as #cores and memory, that map into the different capacity classes.
Note 2: The Throughput of the Virtual appliance really depends on the characteristics of the underlying host and the load by other VMs on the same system.