What is a registry?
A Registry (or Registry Operator) is the company that maintains a database of all domain names registered under a given top-level domain (TLD) such as .com, .design, .dentist, etc. Some registries include Donuts, XYZ, MMX, and Verisign.
Registries differ from registrars (such as Porkbun, GoDaddy, Enom, etc.) in that they do not sell domain names directly to the public. Instead, they are responsible for: maintaining the registry database, wholesale pricing, marketing their portfolio of extensions, and complying with ICANN regulations. Registries are also required to run special DNS servers to host certain records such as "glue" records and the NS records that designate the authoritative nameservers for a domain.