All devices on the Web are recognized by a special number called an IP address, for instance 220.127.116.11. When you have a site, the domain that you type to open it is for your convenience, but the server where the website files are still has an IP address. As there're a lot more websites and devices than there are IP addresses, all the shared hosting servers have a number of sites under an identical IP, whereas when you use a dedicated server you'll be given a dedicated IP as well. Even in the first case though, you are able to obtain a dedicated IP for your websites and host them on a shared server. An advantage would be that you'll enjoy better search engine rankings as a dedicated IP often means a faster loading site. In addition, you need such an IP when you intend to get an SSL certificate for your website and shield the info that your visitors submit on it.