All devices on the Web are recognized by a specific number called an IP address, for instance 220.127.116.11. If you have a site, the domain that you type in order to access it is to save you time, however the server where the site files are still has an IP. Considering that there are many more sites and devices than there are IPs, all shared web hosting servers have a number of websites under an identical IP, while with a dedicated server you'll have a dedicated IP too. Even in the first case though, you will be able to acquire a dedicated IP for your websites and host them on a shared server. One advantage would be that you'll get improved search engine positions as a dedicated IP usually means a faster loading site. What's more, you need such an IP if you want to acquire an SSL certificate for your website and shield the info that your visitors submit on it.