Yes, all plugins and themes purchases have licenses. Single-domain licenses are sub-domain specific. That means if you buy for sub1.domain.com, then the license is not valid for sub2.domain.com. The only exception is for WWW subdomain. So if you buy for www.yourdomain.com, it'll work with both yourdomain.com and www.yourdomain.com.
You should consider multi-domain licenses if you wish to use the themes or plugins on multiple (in fact unlimited) domains or websites.
All products (and derivative works) are non-redistributable.