All devices on the Internet are identified by a specific number called an IP address, for instance 126.96.36.199. When you have a site, the domain that you enter in order to load it is for your convenience, but the server where your website files are still has an IP. Since there are a lot more websites and devices than there're IPs, all the shared hosting servers have a number of sites under the very same IP, whereas using a dedicated server you will have a dedicated IP as well. Even in the first case though, you can acquire a dedicated IP for your websites and host them on a shared server. One benefit would be that you may get far better search engine positions as a dedicated IP usually means a quicker loading website. Also, you need such an IP if you plan to acquire an SSL certificate for your website and protect the data that your visitors submit on it.