What is a Registrar?

A Registrar (or Domain Name Registrar) is an organisation like that has worldwide control in the granting of domains with certain domain name endings (e.g. .com .org .net or Country-specific .uk .de .it .nl etc.)

What is the Registry?

The Registry is the overarching worldwide database that Registrar's have shared access to.

Who is the Registrant?

A Registrant is the person or company who purchases a domain name. For example, Denis O'Regan (Registrant) registers the name thepianoforte.com via Easykey Limited who use Namesco Limited (Registrar) who in turn writes the name to the central database (Registry).

Many of the companies selling domains online are Resellers of the main Registrars.