All devices on the Internet are identified by a specific number called an IP address, for instance 188.8.131.52. When you have a site, the domain that you type to be able to load it is to save you time, yet the server where the website files are still has an IP. As there are a lot more websites and devices than there are IPs, all the shared hosting servers have a number of websites under the very same IP, while using a dedicated server you'll have a dedicated IP as well. Even in the first case though, you're able to obtain a dedicated IP for your sites and host them on a shared server. An advantage would be that you'll enjoy improved search engine rankings since a dedicated IP usually means a quicker loading site. Also, you need such an IP when you would like to buy an SSL certificate for your website and shield the data that visitors submit on it.