The free edition of UpdraftPlus can be installed anywhere and everywhere you like.
When you purchase UpdraftPlus Premium (our version with all extra features, upgrades and 1-year support), then you can choose whether you want a 2-site, 10-site or unlimited site licence. These can be installed on the number of sites indicated!
When you purchase add-ons individually, they are purchased for one site.
The above entitlements are used to grant access to support and access to your UpdraftPlus.Com account for downloading software and obtaining upgrades. UpdraftPlus itself is under the GNU GPL, the same licence as WordPress itself, which grants you many and various further rights.