An Internet Domain Name is a (supposedly) human-readable string that identifies an entity on the Internet, e.g.
Every domain is a name under a Top-Level Domain (TLD). For example, the domain
johndoe.net is the
johndoe name under the
The way to own a domain is to purchase it with a Domain Registrar for an annual fee. TLDs and registrars are regulated by IANA/ICANN.
A domain is yours as long as you pay the fees for it and unless you’re legally obliged to stop using it due to some drastic reason. This is as far as complete ownership goes on the Internet, much like owning a plot of land in the real world and paying annual taxes.
A domain owner can create further subdomains as they please (e.g.
blog.johndoe.net). The original
johndoe.net is known as the apex domain.