What Is a Subdomain? Definition, Examples & SEO Impact
A subdomain is a prefix added to the front of your main domain — the 'blog' in blog.example.com or the 'shop' in shop.example.com. It lets you create a distinct section of your site with its own space, while still belonging to your root domain. This guide explains what a subdomain is, how it differs from a subdirectory, and what the choice means for SEO.
Subdomain, defined
Every web address has parts. In blog.example.com, 'example.com' is the root domain and 'blog' is the subdomain. Subdomains let you carve out separate areas of a website — a blog, a store, a help centre, a regional site — that can run on different systems or be managed by different teams, while still living under one brand.
Technically, search engines and browsers can treat a subdomain as a somewhat distinct site. That distinction is the crux of the SEO debate: is a subdomain part of your main site, or a separate one? The honest answer is 'partly both,' which is why the choice matters.
Subdomain examples
- blog.example.com — a company blog kept separate from the main marketing site.
- shop.example.com — an e-commerce store on a different platform than the main site.
- support.example.com — a help centre or knowledge base, often run on dedicated software.
- app.example.com — the login or web application, separate from the public marketing pages.
- uk.example.com — a country-specific version of a site for a particular market.
Subdomain vs subdirectory
The alternative to a subdomain is a subdirectory (also called a subfolder): example.com/blog instead of blog.example.com. A subdirectory is unambiguously part of your main site, so it inherits the domain's authority directly. A subdomain sits slightly apart, and search engines may treat its authority as partially separate.
For SEO, the general consensus is that subdirectories are the safer default when you want a section to benefit fully from your main domain's authority — a blog or resource centre, for example. Subdomains make sense when a section is genuinely distinct, runs on separate infrastructure, or needs to be managed independently, such as an app, store, or regional site.
Does using a subdomain hurt SEO?
A subdomain will not doom your SEO, but it can make your ranking authority work harder. Because search engines may not pass the full weight of your root domain to a subdomain, content there sometimes has to build its own authority. If your main goal is to rank a content hub and benefit from your existing domain strength, a subdirectory is usually the pragmatic choice. If the section is a distinct product or platform, a subdomain is perfectly reasonable — just be intentional about the trade-off rather than choosing by accident.
Frequently Asked Questions
What is a subdomain?
A subdomain is a prefix added to the front of a main domain, such as 'blog' in blog.example.com. It creates a distinct section of a website that still belongs to the root domain, often used for blogs, stores, help centres, apps, or regional sites.
What is an example of a subdomain?
Common examples include blog.example.com for a blog, shop.example.com for a store, support.example.com for a help centre, and app.example.com for a web application. In each, the word before the main domain is the subdomain.
What is the difference between a subdomain and a subdirectory?
A subdomain sits before the domain (blog.example.com), while a subdirectory is a folder within it (example.com/blog). A subdirectory is unambiguously part of your main site and inherits its authority; a subdomain can be treated as partly separate by search engines.
Is a subdomain bad for SEO?
Not inherently, but a subdomain may not receive the full ranking authority of your root domain, so its content sometimes has to build authority on its own. Subdirectories are the safer default for content hubs; subdomains suit genuinely distinct sections like apps, stores, or regional sites.
Technical SEO
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