All devices on the World Wide Web are identified by a unique number called an IP address, for example 220.127.116.11. If you have a site, the domain that you type to be able to open it is to save you time, however the server where your site files are still has an IP address. Considering that there are many more websites and devices than there are IPs, all shared website hosting servers have a number of sites under the same IP, whereas with a dedicated server you'll get a dedicated IP too. 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 advantage would be that you will have better search engine positions as a dedicated IP generally means a quicker loading site. What's more, you need such an IP if you want to obtain an SSL certificate for your website and protect the info that visitors submit on it.