All devices on the World Wide Web are identified by a special number called an IP address, for example 126.96.36.199. When you have a site, the domain that you type in order to load it is for your convenience, but the server where your site files are still has an IP. Since there're many more sites and devices than there are IP addresses, all the shared hosting servers have a number of sites under an identical IP, whereas using a dedicated server you'll be given a dedicated IP too. Even in the first case though, you will be able to get a dedicated IP for your websites and host them on a shared server. One advantage would be that you may get superior search engine positions since a dedicated IP usually means a quicker loading website. Also, you need such an IP when you intend to buy an SSL certificate for your website and secure the information that your visitors submit on it.