What Is SLD (Second-level domain)? Domain Glossary

Why it matters

The second-level domain is the part you buy, and it carries almost all the value in a sale. When people say they own a name, they mean this label plus its extension. A buyer of brand.com wants the word "brand" under .com, not under another extension. Extensions are separate products with separate owners. A common mistake is assuming owning the .com protects the same label in .net or .ai. It does not. Each combination is a different registration, and a different seller or buyer may hold it.

Source: datatracker.ietf.org

Related terms

Domain name: A domain name is a human-readable address, such as example.com, that points to a website, email server, or other internet service through the Domain Name System. It replaces numeric IP addresses that people cannot easily remember.
Top-level domain (TLD): The top-level domain is the last label in a domain name, the part after the final dot. In icann.org, the TLD is org. It sits at the top of the naming hierarchy of the Domain Name System.
Subdomain: A subdomain is a prefix added to a domain name that creates a separate address under it, such as blog.example.com or shop.example.com. The domain owner creates it with a DNS record at no extra registration cost.
.com: Dot-com is the most widely used top-level domain in the world. Verisign runs the .com registry, and it held about 166.6 million registrations in mid-2026.

All 205 terms

Second-level domain (SLD)

Why it matters

Buying or selling a domain?