All devices on the Internet are recognized by a special number called an IP address, such as 220.127.116.11. When you have a site, the domain name that you type in order to open it is to save you time, but the server where your site files are still has an IP address. Because there're many more websites and devices than there are IP addresses, all of the shared website hosting servers have a number of sites under the same IP, whereas using a dedicated server you'll have a dedicated IP too. Even in the first case though, you're able to acquire a dedicated IP for your websites and host them on a shared server. One advantage would be that you will have superior search engine positions since a dedicated IP usually means a faster loading site. Also, you need such an IP when you intend to obtain an SSL certificate for your website and secure the data that visitors submit on it.