What does Subdomain mean?

A subdomain is a separate part of a main domain used to separate certain content or a section of a website. It looks, for example, like blog.domain.com or help.domain.com. It often serves for a blog, help center, language versions of a website or special sections outside the main content. A subdomain can have its own structure, content and management. In practice, it helps organize a website better and separate different types of pages by their purpose.