Subdomain

A subdomain is a prefix added to your main domain name that creates a separate section of your website or a distinct web service, like blog.example.com or shop.example.com.

Category: General (also: Front End, Infrastructure)

Author: Atomic Glue Technical Team

## Definition

A subdomain is an additional part of your main domain name that lets you organize and separate different sections of your website or host entirely separate web applications under the same root domain. It appears to the left of the second-level domain, separated by a dot. For example, in "developers.atomicglue.com", "developers" is the subdomain. Subdomains are commonly used for blogs (blog.example.com), e-commerce stores (shop.example.com), support portals (help.example.com), or region-specific content (uk.example.com). Each subdomain can point to a different IP address or server, making them a powerful tool for scaling and organizing web infrastructure.

## How Subdomains Work

Subdomains are configured through DNS records, typically A records (pointing to an IP address) or CNAME records (pointing to another domain name). When a browser requests blog.example.com, the DNS system resolves the subdomain separately from the root domain. This means a subdomain can point to a completely different server, hosting provider, or even a third-party platform. For example, a company might host their main website on one server and their e-commerce subdomain on a Shopify-hosted server.

## Subdomain vs Subdirectory

A common architectural decision is whether to use a subdomain (blog.example.com) or a subdirectory (example.com/blog). Subdomains are treated as separate sites by search engines, which can be good or bad depending on your SEO strategy. Subdirectories inherit the authority of the root domain. Use subdomains when you need completely separate infrastructure, technology stack, or team ownership. Use subdirectories when you want consolidated SEO authority and simpler maintenance.

## Common Use Cases

Subdomains are widely used for: * **Separate Applications:** Hosting a web app like a CRM or project management tool under app.example.com. * **Regional Sites:** Serving country-specific content under uk.example.com or de.example.com. * **Development Environments:** Creating staging.example.com or dev.example.com for testing before going live. * **Third-Party Integration:** Pointing a subdomain to a vendor platform like a knowledge base or support ticketing system.

## Common questions

Q: How many subdomains can I create?

A: There is no hard limit, but DNS best practices recommend keeping subdomains manageable. Most hosting providers allow dozens or even hundreds.

Q: Do subdomains affect SEO?

A: Yes. Search engines generally treat subdomains as separate entities from the root domain. This can dilute your SEO authority unless each subdomain is built with its own strong content strategy.

Q: Is www a subdomain?

A: Yes. Technically, www is a subdomain of your root domain. Many organizations choose to redirect www.example.com to example.com (or vice versa) for canonical consistency.

## Key takeaways

• Subdomains create separate, independent sections under your main domain.
• They can point to different servers and hosting providers.
• Subdomains are treated as separate sites by search engines, unlike subdirectories.
• Use them strategically for organization, regional targeting, or isolating different technical stacks.

## Related entries

• [Domain Name](atomicglue.co/glossary/domain-name)
• [TLD (Top-Level Domain)](atomicglue.co/glossary/tld)
• [DNS](atomicglue.co/glossary/dns)

Last updated July 2025. Permalink: atomicglue.co/glossary/subdomain