All devices on the Internet are identified by a specific number called an IP address, for example 220.127.116.11. When you have a website, the domain name that you enter to load it is to save you time, but the server where your site files are still has an IP address. Due to the fact that there're far more websites and devices than there are IP addresses, all shared website hosting servers have a number of sites under the same IP, whereas when you use a dedicated server you'll get a dedicated IP as well. Even in the first case though, you are able to obtain a dedicated IP for your websites and host them on a shared server. An advantage would be that you'll get superior search engine positions as a dedicated IP often means a quicker loading site. Last but not least, you need such an IP in case you want to acquire an SSL certificate for your site and secure the info that visitors submit on it.