All devices on the Web are identified by a specific number called an IP address, for example 188.8.131.52. If you have a site, the domain name that you enter to open it is for your convenience, but the server where your site files are still has an IP address. Since there are many more websites and devices than there're IP addresses, all of the shared website hosting servers have a number of sites under the very same IP, whereas with a dedicated server you will have a dedicated IP as well. Even in the first case though, you're able to acquire a dedicated IP for your sites and host them on a shared server. One advantage would be that you may enjoy far better search engine positions as a dedicated IP generally means a faster loading website. What is more, you need such an IP in case you plan to purchase an SSL certificate for your website and secure the information that visitors submit on it.