Domain
About 5 min read
Last updated: 2026-08-17
What Is a Domain
A domain is the human-readable name of a website, such as example.com or google.co.jp. It serves as an easy-to-remember label for a server's location. During actual communication, DNS translates the domain name into an IP address.
Domain Structure
.com, .jp, .org, etc. Indicates purpose or country.example part of example.com - the label one step to the left of the TLD. This is usually the site's own name, but when the suffix has two levels, such as co.jp, the name sits one label further left (amazon in amazon.co.jp).www or mail, etc. Used to separate services within the same domain.Domains and Phishing Prevention
Phishing scams use domain names that closely resemble legitimate ones. A common trick is placing the real name in a subdomain, such as amazon.co.jp.evil.com.
Read the name from the right. The top-level domain (.com, .jp) plus the label immediately to its left is the part that identifies the registrant, and when the suffix has two levels, such as co.jp, you include one more label. In this example the owner is evil.com, and amazon.co.jp is just a subdomain the owner added at will. Because each registry decides how far its suffix extends, browsers rely on a list called the Public Suffix List to locate that boundary.
When you check a full URL, watch for an @ between :// and the next / as well: there, the host name is whatever follows it, while the part on the left is a field for credentials, which makes it a convenient place to plant a familiar-looking name (an @ later in the URL, inside the path, is just an ordinary character and this rule does not apply).
Domain Registration and Management
Domains are obtained through registrars (domain registration businesses) or their resellers. Fees vary widely by TLD, and first-year discounts are common, so check the renewal price before you register. If a renewal is missed, the domain expires, and once the grace period ends it returns to the pool where someone else can take it.
To learn more about this topic, see also How to Read URLs Safely.
Common Misconceptions
- A .co.jp domain means it's a safe Japanese company
- .co.jp domains are available to Japanese corporations, but being a corporation does not guarantee safety.
- Once you buy a domain, you own it forever
- Domains require annual renewal fees. If you forget to renew, the domain expires.
Domain vs. IP Address
Domain
A human-readable name. Translated to an IP address by DNS.
IP Address
A numerical address used by computers. Used for actual communication.