If you’ve registered a domain but never thought through what each piece is actually called, this is for you. Knowing the vocabulary makes every other domain decision much easier.
The basic structure
Take mail.example.com and read it right to left:
comis the top-level domain (TLD). The rightmost component, after the final dot.exampleis the second-level domain (SLD). What you actually “own” — what you registered at the registrar.mailis a subdomain (also called a third-level domain). Created by you in your DNS settings; the registry has nothing to do with subdomains.
The full string mail.example.com is the fully qualified domain name (FQDN).
TLDs come in three categories
Generic TLDs (gTLDs): .com, .net, .org from 1985, plus the hundreds of new gTLDs added since 2014 (.app, .dev, .xyz, .blog, .shop, etc.).
Sponsored TLDs (sTLDs): .edu, .gov, .mil, .museum — restricted to specific communities with eligibility verification.
Country-code TLDs (ccTLDs): .us, .uk, .de, .fr — tied to a specific country. Some require local presence (.ca, .br); others are open globally (.io, .me, .tv) and get used as quasi-gTLDs.
What you actually buy
When you “register a domain” you’re buying the right to use a specific second-level domain (SLD) under a specific TLD for a specific term (1-10 years).
You’re not buying it forever. You’re paying an annual fee (or 10-year prepay) for exclusive registration. Stop paying and the domain returns to the public pool.
Subdomains are unlimited and free — you can create as many as you want under your registered SLD without paying more.
DNS: turning a name into an address
When someone types example.com into a browser, the Domain Name System resolves the name into the IP address of the server that should respond.
That happens through DNS records you configure at your registrar (or at a separate DNS provider like Cloudflare, AWS Route 53, or DNSimple). The most common record types:
- A record: maps a name to an IPv4 address.
- AAAA record: maps a name to an IPv6 address.
- CNAME record: aliases one name to another (“www points to the apex”, “app points to vercel”).
- MX record: tells mail servers where to deliver email for the domain.
- TXT record: free-text data, used for ownership verification + email auth (SPF, DKIM, DMARC).
- NS record: which nameservers are authoritative for this domain.
Nameservers vs DNS records
These get confused constantly.
Nameservers are the servers that hold your DNS records. Specified at the registrar level (“this domain is managed by ns1.cloudflare.com and ns2.cloudflare.com”).
DNS records are the actual entries that live on those nameservers (“the A record for example.com points at 192.0.2.10”).
Change the nameservers and you switch which provider manages your DNS — but your records have to be re-created on the new provider.
Why this matters in practice
Most domain confusion comes from not knowing which layer owns the problem. If your website is unreachable, you need to figure out: is the registration current? Are the nameservers correct? Are the DNS records correct? Is the server actually running?
Knowing the vocabulary lets you check each layer in order and find the failure fast.