CLS stands for Creative Lighting System and references the entire Nikon wireless flash system.
Nikon CLS wireless communication can control multiple Remote flashes automatically.
The Commander flash is called Master and the Remote flash is called Slave.
I use the build-in flash of Nikon P7700 as Master and a Nikon Sb-800 as a Slave; then I use a Metz 58 AF-1 as Slave.I try to use both as Slaves but they didn't work together.