All devices on the World Wide Web are identified by a specific number called an IP address, for example 123.123.123.123. When you have a site, the domain that you type to load it is to save you time, but the server where the website files are still has an IP address. Due to the fact that there're a lot more websites and devices than there're IPs, all the shared hosting servers have a number of websites under the same IP, while when you use a dedicated server you'll have a dedicated IP as well. Even in the first case though, you can acquire a dedicated IP for your websites and host them on a shared server. One advantage would be that you may get improved search engine positions because a dedicated IP generally means a faster loading site. Furthermore, you need such an IP when you intend to purchase an SSL certificate for your site and secure the data that your visitors submit on it.