All devices on the Internet are identified by a unique number called an IP address, for instance 126.96.36.199. In case you have a site, the domain that you type to open it is to save you time, however the server where the website files are still has an IP address. As there are far more websites and devices than there're IP addresses, all the shared website hosting servers have a number of websites under the same IP, while with a dedicated server you'll have a dedicated IP too. 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 will get superior search engine positions as a dedicated IP often means a faster loading website. Last but not least, you need such an IP when you intend to get an SSL certificate for your site and secure the data that visitors submit on it.