---
obj: concept
wiki: https://en.wikipedia.org/wiki/Domain_name
rfc: https://datatracker.ietf.org/doc/html/rfc1035
---

# Domain
A domain is a human-readable label used to identify a location or an entity on the internet. It serves as a memorable way to reference specific resources, such as websites, servers, or services, rather than relying on numerical [IP](Internet%20Protocol.md) addresses.

Domain names are formed by the rules and procedures of the Domain Name System ([DNS](DNS.md)). Any name registered in the [DNS](DNS.md) is a domain name. Domain names are organized in subordinate levels (subdomains) of the [DNS](DNS.md) root domain, which is nameless. The first-level set of domain names are the top-level domains (TLDs), including the generic top-level domains (gTLDs), such as the prominent domains com, info, net, edu, and org, and the country code top-level domains (ccTLDs). Below these top-level domains in the [DNS](DNS.md) hierarchy are the second-level and third-level domain names that are typically open for reservation by end-users who wish to connect local area networks to the Internet, create other publicly accessible Internet resources or run web sites.

A fully qualified domain name (FQDN) is a domain name that is completely specified with all labels in the hierarchy of the [DNS](DNS.md), having no parts omitted. Traditionally a FQDN ends in a dot (.) to denote the top of the [DNS](DNS.md) tree. Labels in the Domain Name System are case-insensitive, and may therefore be written in any desired capitalization method, but most commonly domain names are written in lowercase in technical contexts.

## Domain Naming Rules
- **Length:** Domain names can be up to 253 characters in length, including the TLD.
- **Characters:** Domains can include letters (a-z), numbers (0-9), and hyphens ("-"). However, they cannot begin or end with a hyphen.
- **Case Insensitivity:** Domain names are not case-sensitive, meaning "example.com" is the same as "Example.com."

## Domain Registration
To use a domain, individuals or entities must register it through domain registrars. The registration process involves selecting an available domain, providing contact information, and paying a registration fee. Registrations are typically renewable on an annual basis.