A subdomain is a subdivision of a larger domain name. It allows website owners to organize and structure their websites hierarchically, facilitating navigation and content organization. Subdomains are commonly used to create separate sections or areas within a website, each with its own unique content or functionality.

In the example you provided, "blog.example.com," the subdomain "blog" is a part of the larger domain "example.com." It serves as a distinct section of the website dedicated to hosting blog content. Visitors can navigate to the blog section by entering "blog.example.com" in their web browser's address bar, accessing content specifically related to the blog.

Subdomains can be used for various purposes, including:

1. Organizing Content: Creating separate subdomains for different types of content, such as blogs, forums, or e-commerce stores.
2. Localization: Using subdomains to serve content tailored to specific geographic regions or languages. For example, "us.example.com" and "uk.example.com" could serve localized versions of a website for users in the United States and the United Kingdom, respectively.
3. Functional Segmentation: Setting up subdomains for specific functions or services, such as "mail.example.com" for email services or "app.example.com" for web applications.
4. Testing and Development: Creating subdomains for testing, development, or staging environments, separate from the live production website.

Overall, subdomains offer flexibility and organization options for website owners, allowing them to create a structured and navigable online presence tailored to their specific needs and goals.