There are three scopes for domains that define the scope we are referring to. The difference needs be clearly understood to avoid confusion.

For a given registered domain example.com we have

1. Root Domain scope - i.e. all links referring from/to *.example.com
2. Sub Domain scope - i.e. all links referring from/to blog.example.com
3. Page scope, or URL scope - i.e. all links referring from/to a specific page https://blog.example.com/links.html
4. TLD referring only to the .com extension.

Sources:

https://moz.com/blog/understanding-root-domains-subdomains-vs-subfolders-microsites

https://moz.com/learn/seo/domain