All devices on the Web are recognized by a unique number called an IP address, for instance 220.127.116.11. When you have a site, the domain that you type to be able to load it is to save you time, however the server where the website files are still has an IP address. Since there are far more websites and devices than there are IPs, all shared web hosting servers have a number of websites under the same IP, while with a dedicated server you'll be given a dedicated IP as well. Even in the first case though, you're able to acquire a dedicated IP for your sites and host them on a shared server. One benefit would be that you will enjoy better search engine positions since a dedicated IP often means a quicker loading website. Furthermore, you need such an IP when you plan to acquire an SSL certificate for your site and secure the info that visitors submit on it.