Registrable domain

A registrable domain is a domain that can be (or has already been) registered by an individual or an organization through a domain name registrar. It’s the highest level domain for a single site on the web.

Registrable domains are created directly underneath an effective top-level domain (eTLD), such as .org, .com, or .ac.uk. For this reason a registrable domain is sometimes called an “eTLD+1”.

For example, all of the following are registrable domains:

All domains under a registrable domain belong to the same organization. For example:

Note that not all eTLDs are top-level domains, because many registrars allow organizations to register domains at levels below the top level. In the example above, .ac.uk is a subdomain of the top-level .uk domain, so sussex.ac.uk and aber.ac.uk can be registered to different organizations.