All devices on the Internet are identified by a special number called an IP address, for instance 220.127.116.11. When you have a site, the domain that you type in order to load it is for your convenience, but the server where the site files are still has an IP address. Since there are many more websites and devices than there are IP addresses, all the shared website hosting servers have a number of sites under an identical IP, while using a dedicated server you'll be given a dedicated IP as well. Even in the first case though, you are able to acquire a dedicated IP for your websites and host them on a shared server. One benefit would be that you will get far better search engine rankings because a dedicated IP generally means a faster loading site. Furthermore, you need such an IP in case you want to buy an SSL certificate for your site and secure the info that your visitors submit on it.