What is a domain name?

A domain name is the address people type to reach something you put on the internet, like yourbusiness.com. Computers find each other using numeric IP addresses; a domain name is the human-readable name that stands in for one, and the Domain Name System is what translates between the two. Every domain name is unique across the entire internet, which is why registering one takes it off the market for everyone else.

What a domain name actually is

Every machine that serves something on the internet is reachable at a numeric address, an IP address. Those numbers work fine for machines and badly for people. So the internet runs a global directory that maps names people can remember onto the numbers machines actually use. That directory is the Domain Name System, specified in 1987 and still the same idea today, and the names in it are domain names.

The important consequence is uniqueness. There is exactly one example.com in the world. When you register a name, you are not buying a copy of it; you are taking the only one there is, and no one else can register that exact string while your registration stands. That is what makes a domain name worth having early: it is the one part of what you are building that someone else can take first.

The parts of a domain name

Read a domain name right to left, because that is the order the system resolves it in. Take shop.yourbusiness.com:

• .com is the extension, also called the top-level domain or TLD. It is the rightmost part, and it sits at the top of the hierarchy. There are well over a thousand of them in the IANA root zone, from the familiar .com and .org to country endings like .uk and newer ones like .ai and .io.
• yourbusiness is the label you choose. Together with the extension it forms the registrable domain, yourbusiness.com. This is the piece you actually register, and the piece that becomes your name.
• shop is a subdomain. Once you hold yourbusiness.com you can create subdomains under it yourself, as many as you want, without registering anything further. shop.yourbusiness.com, blog.yourbusiness.com and app.yourbusiness.com are all yours by virtue of holding the one name.

The www at the front of an address is just a subdomain by convention, not a required part of a domain name. It is why example.com and www.example.com usually lead to the same place: someone configured both.

Domain name, URL, website

These three get used interchangeably and they are not the same thing. In https://justdomain.ai/learn, https is the scheme, justdomain.ai is the domain name, and /learn is the path to one specific page. The URL is the full address of a page; the domain name is the part that identifies whose corner of the internet it is. The website is the content that gets served when someone arrives. For the practical split between the address and the thing at the address, see domain vs hosting.

How the address finds your site

When someone types your name into a browser, a short lookup happens before any page loads:

1. The browser asks a resolver for the address behind yourbusiness.com.
2. The resolver works down the hierarchy: the root servers point it at the servers for the .comextension, which point it at the specific nameservers holding your name’s records.
3. Those nameservers answer with the actual records you set: the IP address behind an A record, another name behind a CNAME, your mail provider behind an MX record.
4. The browser connects to that destination and the page loads.

All of that normally happens in well under a second. The part that matters to you is step three: the records are yours to set, and they are what decides where your name points. Changing them is how you move what you built from one provider to another without your address ever changing. If you want the record types in one line each, DNS records, explained covers them.

Who actually runs domain names

Three roles sit behind every registered name, and knowing which is which explains a lot about how the industry behaves:

• The registryoperates one extension and holds the authoritative list of every name registered under it. Verisign runs .com; each extension has its own registry, and the registry sets that extension’s rules and its wholesale rate.
• The registrar is the company accredited to submit registrations to registries on behalf of customers. For generic extensions that accreditation comes from ICANN.
• The registrant is you: the person or company the registration is recorded to.

Just Domain is a reseller that partners with ICANN-accredited registrars. The registry sees your registration the same way it would going direct: you own the registration and can transfer it to another registrar, subject to the standard ICANN 60-day post-registration transfer lock.

This structure is also why the same name can cost noticeably different amounts at different companies. Every registrar reaches the same registry and gets the same underlying record. What differs is what each one adds on top, and what it tries to sell you alongside it.

What a domain name is allowed to contain

The rules are older and stricter than most people expect, and they are worth knowing before you fall in love with a name:

• Letters, digits and hyphens. No spaces, no underscores, no punctuation. A hyphen cannot start or end a label.
• 63 characters per label, 255 for the whole name. These limits come from the original DNS specification, RFC 1035, and every registry still enforces them.
• Case does not matter. Example.com and example.com are the same name. Capitals on a business card are a styling choice, nothing more.
• Other scripts are supported, indirectly. Internationalised domain names let a name be written in Arabic, Hebrew, Chinese or any other script; the system encodes it into that same restricted character set underneath, which is why such names sometimes appear as a string starting with xn--.

Within those rules, the useful test is spoken, not written: say the name out loud to someone and see whether they can type it without asking how it is spelled. Hyphens and digits are where that test usually fails. There is more on this in how to choose a domain name.

Getting one

Registering a name is the short part. The name you want either is or is not already taken, and the only way to know is a live check against the registry, right now, for the exact string.

1. Check the exact name live. Not a list you saw last month. Availability moves constantly.
2. Pick the extension that fits. .com is the default people assume; .ai and .io read as technical; a country ending signals where you operate. See domain extensions, explained.
3. Register it, then point it. The name is yours from the moment the registration lands. Where it points is a records question you can answer the same day or a month later.

Domain availability changes constantly. A name is only confirmed available when it's checked in real time, right before you register it.

I'm building [what you're building] and I need a domain name for it. Explain in plain terms what I'm actually registering, then check live availability for a few name ideas across the endings that fit, and show me a checkout link for any that are free.