The activations refer to the installation of Design Extender.
when you install Design Extender and use it in Dreamweaver, you have to first activate it.
The licensing allows you to activate Design Extender on 2 computers, for example: using design Extender on a Lap Top and a Desktop computer.
On those 2 computers you can use design extender to build as many web sites as you like. There is not a limitation to the number of web sites that can be built, only the number of platforms you use to build those sites.
If you uninstall Design Extender form one of those computers, you can visit the all my downloads page to clear activations, then install design extender on a new computer.