A subdomain is a portion or division of a more extensive domain frequently used to group and classify various website elements. A prefix, denoted by a dot (. ), is added to the primary domain name to establish a subdomain, as in "subdomain.example.com". A website can have numerous parts, each with its content and URL, while still preserving the overall identity of the primary domain.

For instance, a business might use a subdomain for a particular product, like "product.example.com," or for its blog, like "blog.example.com". Subdomains can also have separate hosting, security, and content management systems and can be controlled independently of the main domain.