The difference between sub-domains and VHosts is important to understand because it can affect the way your website is accessed and how search engines index your website. If you are not using the correct type of hosting, it can also affect the speed and performance of your website and even be vulnerable to cybersecurity vulnerabilities like DNS hijacking, SSL certificate vulnerabilities, and cross-site scripting.

Subdomain

A sub-domain is a second-level domain that is part of a larger domain. For example, if you have a website at example.com, you can create a subdomain at subdomain.example.com. A subdomain can be used to create a separate website, or it can be used to point to a different website or directory on the same server.

Virtual Host

A Virtual Host (VH) is an Internet hosting service that allows organizations to host their websites on a single server. A VH can be used to host multiple websites, each with its own domain name, or it can be used to host multiple websites that share the same domain name. VHosts may or may not have public DNS records, so in order to access your site, you may need to change host names and addresses on your localhost (typically located in etc/hosts) or use the Host: header of a standard HTTP request.

In conclusion, it is important to understand the difference between sub-domains and VHosts in order to ensure that your website is accessible and performing optimally.