All devices on the Web are identified by a specific number called an IP address, for instance 220.127.116.11. If you have a site, the domain name that you type to be able to load it is for your convenience, but the server where the website files are still has an IP. As there are far more sites and devices than there are IPs, all the shared hosting servers have a number of websites under an identical IP, whereas with a dedicated server you'll have a dedicated IP as well. Even in the first case though, you are able to obtain a dedicated IP for your sites and host them on a shared server. One advantage would be that you'll enjoy superior search engine rankings as a dedicated IP often means a faster loading site. Last but not least, you need such an IP if you want to acquire an SSL certificate for your site and protect the data that your visitors submit on it.