All devices on the Internet are recognized by a special number called an IP address, for instance 126.96.36.199. If you have a site, the domain that you enter in order to access 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 are far more sites and devices than there're IPs, all of the shared hosting servers have a number of sites under the very same IP, while using a dedicated server you will have a dedicated IP too. Even in the first case though, you'll be able to get a dedicated IP for your websites and host them on a shared server. One advantage would be that you'll enjoy better search engine positions since a dedicated IP generally means a quicker loading site. Also, you need such an IP if you plan to get an SSL certificate for your website and secure the information that your visitors submit on it.