All devices on the Web are identified by a specific number called an IP address, for instance 188.8.131.52. In case you have a website, the domain name that you enter to access it is for your convenience, however the server where your website files are still has an IP. Since there're a lot more websites and devices than there're IPs, all shared website hosting servers have a number of sites under the very same IP, while with a dedicated server you'll be given a dedicated IP as well. Even in the first case though, you will be able to acquire a dedicated IP for your sites and host them on a shared server. One advantage would be that you will get better search engine rankings as a dedicated IP often means a quicker loading website. What is more, you need such an IP when you would like to get an SSL certificate for your website and shield the information that your visitors submit on it.