All devices on the Web are recognized by a unique number called an IP address, for example 220.127.116.11. When you have a site, the domain name that you enter in order to access it is for your convenience, but the server where the website files are still has an IP address. Because there are a lot more websites and devices than there're IPs, all shared web hosting servers have a number of sites under the very same IP, while with a dedicated server you'll get a dedicated IP as well. Even in the first case though, you can get a dedicated IP for your websites and host them on a shared server. One benefit would be that you'll enjoy far better search engine rankings because a dedicated IP generally means a faster loading site. In addition, you need such an IP when you would like to purchase an SSL certificate for your website and secure the data that your visitors submit on it.