All devices on the Internet are identified by a unique number called an IP address, for example 220.127.116.11. When you have a website, the domain that you enter to be able to open it is to save you time, yet the server where the website files are still has an IP address. Since there are many more websites and devices than there're IPs, all the shared web hosting servers have a number of sites under the very same IP, whereas when you use 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 websites and host them on a shared server. An advantage would be that you will have improved search engine positions as a dedicated IP usually means a faster loading site. Furthermore, you need such an IP if you would like to purchase an SSL certificate for your website and protect the information that your visitors submit on it.