A subdomain is a web address structure created under a main domain by adding a section before the root domain name. In a domain structure, the main domain represents the root domain, while a subdomain is used to create a separate section, service, content area or application under that main domain. For example, if kriko.io is the main domain, blog.kriko.io, shop.kriko.io, support.kriko.io or tr.kriko.io are examples of subdomains. In contrast, an address such as kriko.blog is not a subdomain; it is a separate domain name.
A subdomain should not be confused with a subdirectory. blog.kriko.io is a subdomain example. kriko.io/blog is a subdirectory example. Similarly, kriko.io/tr is not a subdomain; it is a folder or URL path under the main domain. This distinction is important for technical setup, SEO and site architecture. Subdomains and subdirectories can create different requirements for management, measurement and optimization.
Although subdomains are connected to the main domain, they can technically be configured like separate websites or applications. They can be hosted on different servers, managed with different CMS platforms, use different designs or run on separate technical infrastructures. For this reason, subdomains allow brands to manage different digital assets under the main domain while keeping them operationally more separate.
Subdomains can be used for many different purposes. A blog, support centre, help documentation, online store, careers page, dealer panel, customer portal, education platform, application interface or country/language-based site structure can be built on a subdomain. For example, support.example.com can be used for a support centre, careers.example.com for a human resources page and app.example.com for a web application where users log in.
Subdomains can also be used for blog structures. A brand may publish its content under blog.example.com. However, using a subdomain for a blog is not mandatory. The same blog structure can also be created under the subdirectory example.com/blog. The right choice depends on SEO strategy, technical infrastructure, CMS needs, content management, security, performance and the operational requirements of the teams involved.
From an SEO perspective, subdomains should be evaluated carefully. Subdomains are connected to the main domain, but search engines do not always treat them as simple extensions of the main website. A subdomain’s technical setup, content quality, internal linking structure, backlink profile and user experience also matter. Therefore, launching a blog on a subdomain does not automatically mean that it will strengthen the SEO performance of the main domain.
There is no single correct answer between using a subdomain and a subdirectory for SEO. In some projects, a subdirectory structure may be more efficient because the content remains within the integrated site architecture of the main domain. In other projects, a subdomain may make more sense because the content or application needs to be separated technically, operationally or strategically from the main site. Product documentation, SaaS applications, dealer portals or global country sites can be examples where subdomains may be preferred.
Subdomains can also be used by companies that operate in different locations. For example, if a company wants to create a separate structure for each country or region, it can use subdomains such as tr.example.com, de.example.com or us.example.com. Similarly, a company may create subdomains for dealers in different cities. However, for local SEO, this decision should be made together with Google Business Profile structure, location pages, content management and technical sustainability.
Holdings, multi-brand organizations and companies operating in different business lines may also use subdomains. For example, a company may keep its corporate website on example.com, while managing human resources under career.example.com, investor relations under investor.example.com, support under support.example.com and the customer panel under panel.example.com. This structure can make it easier for different teams or systems to operate independently.
Owning a domain name alone is not enough to create and run a subdomain; DNS management and the technical infrastructure where the subdomain will point are also needed. A subdomain is usually created through a domain management panel, DNS provider, hosting panel, CDN or cloud infrastructure. For example, a DNS record is created for blog.example.com, and this record is pointed to the relevant server, hosting, CDN or application infrastructure. To actually publish a site, hosting infrastructure or a related service setup is required.
The number of subdomains that can be created may vary depending on the domain registrar, DNS provider, hosting package or infrastructure limitations. Some providers allow many subdomains, while others may limit them based on the selected package. For this reason, subdomain planning should consider not only naming, but also infrastructure capacity, SSL certificates, security settings, redirect structure and ease of management.
Measurement should also be planned carefully when using subdomains. Google Analytics, Google Tag Manager, advertising pixels, cookie permissions, Search Console verification and conversion tracking should be configured correctly according to the subdomain structure. For example, if a user moves from the main site to app.example.com, incorrect cross-domain or subdomain tracking settings can split sessions, distort source/medium data or attribute conversions to the wrong channel.
Subdomains are also important from a security perspective. SSL certificates, access controls, security headers, cookie scope and application security should be evaluated separately for each subdomain. Even if the main domain is secure, a poorly configured subdomain can create security risks. Old, forgotten or unused subdomains should be reviewed regularly and closed when necessary.
One of the most important points in subdomain usage is avoiding unnecessary fragmentation. Creating a separate subdomain for every content type or campaign can make site architecture complicated. User experience, SEO authority, content management and measurement may become fragmented. Therefore, before choosing a subdomain, the key question should be: “Does this structure really need to be managed separately from the main site?” If the content is strongly connected to the main site and serves the same SEO strategy, a subdirectory may be more suitable.
In summary, a subdomain is a web address structure that works under a main domain and is created by adding a section before the domain name. Addresses such as blog.example.com, support.example.com or app.example.com are examples of subdomains. Subdomains can be used for blogs, support centres, applications, dealer structures, country or language sections, customer panels and different business units. When used correctly, they can simplify technical management, but they should be planned carefully in terms of SEO, measurement, security and user experience.
