A: Hi, I confuse myself sometimes as well. :) but it's actually simple:

1) you get one license key that lasts a lifetime
2) the license key can be activated on 2 sites, which enables that site to receive one click updates of the MD theme and official drop-ins (similar to plugins but easier)
3) as a bonus: you can use MD on as many sites as you own but only your licensed sites are eligible for one click updates

I realize now the listing is out of date, and this final AppSumo offer is for one lifetime license key for 2 site activation (ignore the number 5 for this deal).

I hope that helps!

- Alex