All devices on the Web are identified by a specific number called an IP address, for instance 220.127.116.11. When you have a website, the domain that you enter to access it is to save you time, however the server where the site files are still has an IP. Considering that there're many more sites and devices than there're IP addresses, all of the shared web hosting servers have a number of websites under the very same IP, whereas using a dedicated server you'll have a dedicated IP too. Even in the first case though, you will be able to get a dedicated IP for your sites and host them on a shared server. An advantage would be that you'll enjoy far better search engine positions as a dedicated IP usually means a faster loading website. What's more, you need such an IP when you want to obtain an SSL certificate for your site and shield the data that your visitors submit on it.