miji.beA subdomain is a string added before the main (root) domain, separated by a dot. In "blog.example.com," "blog" is the subdomain. Once you own a domain, you can create unlimited subdomains at no additional cost.
Common uses for subdomains include separating website functions: "www.example.com" for the main site, "blog.example.com" for the blog, "shop.example.com" for e-commerce, and "api.example.com" for API endpoints. Google uses this pattern extensively with "mail.google.com," "drive.google.com," and "docs.google.com."
From an SEO perspective, the subdomain vs. subdirectory (example.com/blog/) debate has persisted for years. Google's John Mueller has stated that Google can handle both properly, but in practice many people report that subdirectories consolidate domain authority more effectively, and new or smaller sites often default to subdirectories. Treat that as experience-based guidance rather than a rule that guarantees better rankings.
Subdomains are commonly used when setting up custom domains for URL shortening services. Creating a subdomain like "link.mycompany.com" or "go.mycompany.com" and pointing it via CNAME record to the shortening service lets you leverage your brand's domain authority while maintaining a dedicated namespace for short links.
Technically, DNS allows independent record configuration for each subdomain. You can host your main site and blog on different servers, or use different CDN providers for each. This flexibility is the subdomain's greatest strength.