All devices on the Internet are identified by a special number called an IP address, such as 126.96.36.199. When you have a site, the domain name that you type in order to load it is for your convenience, however the server where the website files are still has an IP. Due to the fact that there're far more websites and devices than there are IP addresses, all of the shared web hosting servers have a number of websites under an identical IP, while using a dedicated server you'll be given 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 will have better search engine rankings since a dedicated IP usually means a faster loading website. In addition, you need such an IP in case you intend to buy an SSL certificate for your site and secure the data that your visitors submit on it.