Web & Networking › Networking Fundamentals

Domain Name

A human-readable address like example.com.

Also known as: domain, hostname, DNS name, FQDN

A domain name is a human-readable address on the internet, like example.com. People remember names far more easily than numbers, and the DNS system translates a name into the IP address a computer needs.

https://shop.example.com/products
        └─┬─┘ └───┬───┘ └┬┘
     subdomain  second-level  top-level domain (TLD)
                domain

Read right to left:

• Top-level domain (TLD): .com, .org, .id, .dev, country codes like .uk.
• Second-level domain: the part you register: example.
• Subdomain: anything you add in front: shop, api, www.

A full name including all parts is a fully qualified domain name (FQDN).

Owning one

You register a domain through a registrar for a period (usually yearly), and then control its DNS records, which say where the name points (DNS record types). You can create as many subdomains as you like under a domain you own.

example.com        → A record → 93.184.216.34
api.example.com    → CNAME   → my-service.cloud-provider.com

Things to know

• A domain is not a website. You still need a server, and DNS records pointing at it.
• Changes take time to spread, because of caching (DNS TTL).
• HTTPS certificates are issued for specific names (and wildcards), and expire (SSL certificates).
• Subdomains and the browser’s security: cookies and the same-origin policy treat different subdomains differently (same-origin policy).
• Domains expire. Letting one lapse can lose your site and email, and let someone else take it over.
• Names are case-insensitive, and international names use an encoded form.
• Look-alike domains are used in phishing, so be careful with user-supplied URLs.

localhost is a special name for your own machine (localhost).