All devices on the Web are recognized by a specific number called an IP address, for example 188.8.131.52. When you have a site, the domain name that you enter to open it is to save you time, however the server where the site files are still has an IP address. Because there're a lot more sites and devices than there are IPs, all of the shared web hosting servers have a number of websites under the very same IP, while when you use a dedicated server you'll get a dedicated IP as well. Even in the first case though, you can obtain a dedicated IP for your websites and host them on a shared server. An advantage would be that you will have superior search engine rankings because a dedicated IP usually means a faster loading website. In addition, you need such an IP in case you intend to obtain an SSL certificate for your site and protect the information that visitors submit on it.