Hmm. okay, I will try to explain...

Wayland is a new window manager, it's a development to (evantually) replace X11 in unix/linux systems.
X11 is really old piece of software, it was new when I learned Unix and you need to belive that was long long time ago
X has been extended way beyond it's architechtural limits, and it is time to get a newly designed, sleeker system.

Now, currently Nemo and Harmattan both use X11. That's basically what draws up your screen in the device and does a lot of other things behind the scenes too.

Nemo is currently swithcing to use Wayland, which means a lot of things need to be changed. This is still experimental, there are no ready-made images to use, you need to tweak your device a lot to make it work.

Eventually (I hope) it will be possible to install Nemo with full Wayland support and all applications just as you install it now, as a FS image but that will take some time still.