Domain name glossary
The words behind the endings, explained in a sentence or two — with real examples from the root zone.
TLD (top-level domain)
TLD stands for top-level domain: the last part of a domain name, after the final dot. In "example.com" the TLD is .com. Every TLD is listed in the DNS root zone, which IANA maintains.
ccTLD (country-code top-level domain)
A ccTLD is a country-code top-level domain: a two-letter TLD reserved for a country or territory, taken from the ISO 3166-1 list. .de is Germany, .jp is Japan, .tv is Tuvalu. Since 2010 some countries also have ccTLDs in their own script, like .рф.
gTLD (generic top-level domain)
A gTLD is a generic top-level domain — any TLD that isn't tied to a country, like .com, .org, .app or .pizza. gTLD registries operate under contracts with ICANN, and names are sold through ICANN-accredited registrars.
sTLD (sponsored top-level domain)
A sponsored TLD is a specialized generic TLD with a sponsor that represents a particular community — air transport for .aero, cooperatives for .coop, museums for .museum. The sponsor sets eligibility rules for who may register.
Brand TLD (dotBrand)
A brand TLD is a top-level domain owned and used by one company for its own sites, like .google, .bmw or .apple. Under Specification 13 of ICANN's registry agreement, the owner keeps every name for itself, so the public can't register them.
Domain hack
A domain hack uses the TLD as part of a word or phrase, so the whole address spells something: del.icio.us, bit.ly, youtu.be. Most hacks use country codes whose letters happen to fit, like .ly, .io or .me.
IDN & Punycode
An internationalized domain name (IDN) uses characters beyond A–Z, like ü, я or 中. The DNS itself only stores ASCII, so IDNs are converted to Punycode: an ASCII form that starts with "xn--". The TLD .рф, for example, is stored as xn--p1ai.
Second-level domain (SLD)
The second-level domain is the part directly left of the TLD — "example" in example.com. Some registries also create second-level spaces such as .co.uk or .com.au, which is why those look like TLDs but aren't.
Special-use domain name
Special-use domain names are reserved so they never resolve on the public internet: .test and .example for testing and documentation, .localhost for your own machine, .local for multicast DNS, .onion for Tor, .internal for private networks.
Registry vs. registrar
A registry runs a TLD — it keeps the database of every name under it, like Verisign for .com. A registrar is the company you buy a domain from; it sends your registration to the registry. For gTLDs, registrars are accredited by ICANN.
DNS root zone
The root zone is the top of the DNS: the list of every top-level domain and the name servers for each one. IANA maintains its contents, and it's served to the world by root servers under 13 names, a.root-servers.net through m.root-servers.net.
DNSSEC
DNSSEC adds cryptographic signatures to DNS answers, so a resolver can check that they weren't forged or altered. For a TLD to be "DNSSEC-signed", the root zone must hold a DS record for it, linking the chain of trust from the root down.