Domain hierarchy refers to the structure of domain names and how they are organized within the Domain Name System (DNS). The domain hierarchy consists of different levels, with each level separated by a period or "dot." Here's a breakdown of the domain hierarchy from top to bottom:
1. Root domain: The root domain is the highest level in the domain hierarchy and is represented by an empty string or a single dot (.) at the end of a domain name. Every domain name ultimately ends with the root domain, although it is not usually shown when typing or displaying domain names.
2. Top-Level Domain (TLD): TLDs are the first level below the root domain in the hierarchy. There are two types of TLDs: generic top-level domains (gTLDs) and country-code top-level domains (ccTLDs). Examples of gTLDs include .com, .org, and .net, while ccTLDs are two-letter codes assigned to specific countries or territories, such as .in for India, .us for the United States, and .uk for the United Kingdom.
3. Second-Level Domain (SLD): SLDs are the next level below TLDs and are the most recognizable part of a domain name. This is the custom name you choose when registering a domain, such as "example" in example.com. SLDs are unique within their respective TLDs and are often used to represent a specific organization, brand, or individual.
4. Third-Level Domain (also known as a subdomain): Third-level domains are optional and are used as an additional layer of organization below the second-level domain. Subdomains can be created to separate different sections of a website or to host multiple sites under one domain. An example of a third-level domain is "blog" in blog.example.com.
5. Fourth-Level Domain and beyond: It's possible to create even more specific domains by adding additional levels, although this is not very common. These domains are sometimes used for specific applications or for internal network organization. An example of a fourth-level domain could be "dev" in dev.blog.example.com.
In summary, the domain hierarchy is a structured system that organizes domain names from the most general (root domain) to the most specific (subdomains) level. This hierarchical structure ensures that domain names are unique and easily identifiable on the internet.