There are key role differences between registry, registrar and registrant.
Registry is an organisation or a company that is acting as the official administrator to govern and manage the domain extension.
Registrar is an organisation or a company that technically and operationally qualified and capable to provide domain registration service as well as domain management tools. It has to be a proven trustworthy entity for being the intermediate company between the registry and the registrant and GetYour.iD is a registrar that you can trust to register and secure your Internet Identity.
Registrant is a person or a company who register for a domain name. When the domain name is registered successfully, the domain name will be awarded to the person or the company. They will then the owner of the domain name and have the full right to use the domain name for the period of registration term selected.