All devices on the Internet are identified by a special number called an IP address, for example 123.123.123.123. If you have a website, the domain name that you enter to access it is to save you time, but the server where your site files are still has an IP. Because there are far more sites and devices than there are IPs, all of the shared hosting servers have a number of sites under the same IP, while using a dedicated server you'll get a dedicated IP too. Even in the first case though, you can obtain a dedicated IP for your sites and host them on a shared server. An advantage would be that you may get better search engine positions because a dedicated IP usually means a faster loading site. Last but not least, you need such an IP in case you want to buy an SSL certificate for your site and secure the data that your visitors submit on it.