Virtual VS Virtual-Address

virtual -> This is the Virtual Server (VS) which you create with a name followed by destination of IP:PORT, assigning pool, profiles, etc.

virtual-address -> This is the part of VIP settings, where you can name a VIP and then use that name to create a VS (Similar to node creation with name & use that name in the pool member creation).

(tmos) create ltm virtual-address test-virtual-address-name address 21.21.21.12
(tmos) create ltm virtual dummy_virtual-address destination test-virtual-address-name:80
(tmos) list ltm vi
Components:
  virtual           virtual-address
(tmos) list ltm virtual dummy_virtual-address
ltm virtual dummy_virtual-address {
    destination test-virtual-address-name:http
    mask 255.255.255.255
    profiles {
        fastL4 { }
    }
    source 0.0.0.0/0
    vs-index 234715
}

Modify the other properties of address too (icmp, traffic group), lets say you have 10VS (1.1.1.1:80,1.1.1.1:443,1.1.1.1:53 etc) on the same Vip(1.1.1.1) address, you can modify the vip-address to reflect the changes on the all 10VS.