All devices on the Web are recognized by a unique number called an IP address, for instance 123.123.123.123. In case you have a website, the domain that you type to open it is for your convenience, yet the server where the website files are still has an IP. As there are many more sites and devices than there're IPs, all the shared web hosting servers have a number of sites under the same IP, while with a dedicated server you will have a dedicated IP too. Even in the first case though, you are able to acquire a dedicated IP for your websites and host them on a shared server. One advantage would be that you'll get better search engine rankings since a dedicated IP often means a faster loading website. Furthermore, you need such an IP in case you want to buy an SSL certificate for your website and secure the data that visitors submit on it.