All devices on the Web are recognized by a specific number called an IP address, for instance 220.127.116.11. When you have a site, the domain that you type in order to open it is for your convenience, but the server where your site files are still has an IP. Due to the fact that there are a lot more sites and devices than there're IPs, all the shared website hosting servers have a number of websites under the same IP, while with 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 sites and host them on a shared server. An advantage would be that you will have far better search engine rankings since a dedicated IP generally means a faster loading site. Last but not least, you need such an IP when you plan to obtain an SSL certificate for your website and shield the info that visitors submit on it.