All devices on the Internet are recognized by a unique number called an IP address, for instance 220.127.116.11. In case you have a website, the domain that you type in order to load it is to save you time, however the server where the site files are still has an IP. Because there're many more websites and devices than there are IPs, all shared website hosting servers have a number of websites under an identical IP, whereas when you use a dedicated server you'll be given a dedicated IP too. Even in the first case though, you'll be able to get a dedicated IP for your websites and host them on a shared server. An advantage would be that you may get far better search engine positions because a dedicated IP generally means a quicker loading site. Last but not least, you need such an IP in case you plan to buy an SSL certificate for your website and protect the info that your visitors submit on it.