A subdomain is a prefix added before your domain to create a separate section or site — for example blog.example.com or shop.example.com. You own the registered domain (example.com) and can create as many subdomains under it as you like, for free, through your DNS settings. Even www is a subdomain. It is distinct from a subfolder like example.com/blog, which is a path within one site.
Subdomains are one of the most useful and least understood parts of owning a domain. They let you carve a single registered name into multiple independent areas — a blog here, a shop there, a help centre somewhere else — without buying anything extra. Here is how they work and when to reach for one.
What is a subdomain?
A subdomain is simply an extra label to the left of your domain. Reading a web address right to left, you start at the TLD, then the second-level domain you registered, and anything further left is a subdomain. In blog.example.com:
.comis the TLD,exampleis the second-level domain you registered,blogis the subdomain — a section you created under your own domain.
Because you control everything under the domain you registered, you can invent subdomains at will: blog., shop., app., help., api. — each pointing wherever you choose. No new registration, no extra fee.
An additional label placed before a domain name (e.g. blog in blog.example.com), used to create distinct sections or sites under one registered domain, managed through DNS.
How do subdomains work?
Subdomains are created and steered through DNS, the system that maps names to servers. When you add a subdomain in your DNS or hosting panel, you create a record that tells the internet where that prefix should point — it can lead to the same server as your main site, a completely different server, or a third-party service.
This is why subdomains are so flexible: shop.example.com might run on an e-commerce platform, blog.example.com on a separate blog host, and example.com on your own server — all under one registered name. To see where this sits in the bigger picture of name resolution, read how the DNS hierarchy works.
Yes, www is a subdomain
www.example.com is technically a subdomain of example.com. It is just the oldest and most familiar one. Most sites configure www and the bare domain to lead to the same place, which is why you rarely think of it as a subdomain at all.
Subdomain vs subfolder: what's the difference?
This is the comparison that trips people up. Both organise content, but they work differently:
| Subdomain | Subfolder | |
|---|---|---|
| Example | blog.example.com | example.com/blog |
| Where it lives | A prefix, set in DNS | A path on the same site |
| Can host a separate system? | Yes | No — same site |
| Extra cost? | No | No |
| Typical use | Distinct apps, platforms, sections | Closely related content in one site |
Rule of thumb: use a subdomain when the content is genuinely a separate system or experience; use a subfolder when it is part of the same site and you want it to share the main site’s structure and authority.
What are subdomains used for?
Common, practical uses include:
- Distinct platforms —
shop.for an online store,app.for a web app. - Support and docs —
help.ordocs.on a dedicated help system. - Technical endpoints —
api.for an API,cdn.for asset delivery. - Environments —
staging.ordev.for testing before changes go live. - Regional or language splits — though many sites use subfolders for these instead.
Are subdomains good or bad for SEO?
Neither, inherently. Search engines index subdomains without trouble. The subtlety is that a subdomain can be treated as a somewhat separate entity from your main domain. For content closely tied to the main site, many owners prefer a subfolder so that all signals consolidate on one domain. For genuinely distinct properties — a separate app, a community, a regional site — a subdomain is perfectly appropriate.
The decision should follow the content, not a blanket rule: keep tightly related material together in subfolders, and use subdomains when something is truly its own thing. None of this changes the fundamentals of your domain name itself.
★ Key takeaways
- A subdomain is a free prefix (
blog.example.com) you create under your registered domain. - Subdomains are configured in DNS and can point to entirely separate servers or services.
wwwis itself a subdomain — just the most familiar one.- Use subdomains for genuinely separate systems; use subfolders for closely related content.
Frequently asked questions
What is a subdomain in simple terms?
A subdomain is a prefix you add to your domain to create a separate area — for example blog.example.com or shop.example.com. You own example.com, and you can create as many subdomains under it as you like, for free, through your DNS settings.
Is www a subdomain?
Yes. www is technically a subdomain of your domain — www.example.com is a subdomain of example.com. It is so conventional that browsers and sites usually treat www and the bare domain as the same destination, but structurally it is a subdomain like any other.
What is the difference between a subdomain and a subfolder?
A subdomain is a prefix (blog.example.com); a subfolder (or subdirectory) is a path on the same site (example.com/blog). Subdomains are configured in DNS and can host separate sites or systems; subfolders are just paths within one site. Both are valid — the choice affects structure and, sometimes, SEO strategy.
Do subdomains cost extra?
No. Subdomains are free. Once you have registered a domain, you can create subdomains yourself in your DNS or hosting control panel at no additional cost. You are only ever charged for the registered domain itself, not for the subdomains you build under it.
Are subdomains bad for SEO?
Not inherently. Search engines can index subdomains perfectly well. The nuance is that a subdomain is sometimes treated as a somewhat separate entity from the main domain, so for closely related content many sites prefer a subfolder to keep authority consolidated. The right choice depends on how distinct the content is.