A sub-domain is a domain name that is part of a larger domain name. For example, the sub-domain of "www.example.com" could be "blog.example.com". The sub-domain is separated from the larger domain name by a dot (.) symbol.
Sub-domains are often used to create separate websites within a domain name. This can be useful for organizing content, or for providing different services or features on different websites. For example, a company might use a sub-domain for its blog, its e-commerce store, and its corporate website.
In some cases, a sub-domain can also be used to target a specific audience. For example, a website might use a sub-domain for a Spanish language version of its website, in order to reach Spanish-speaking customers.
When creating a sub-domain, it's important to make sure that the domain name is available. To do this, you can use a domain name availability checker.