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 to access it is for your convenience, yet the server where your site files are still has an IP. Because there're far more websites and devices than there're IP addresses, 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 can acquire a dedicated IP for your websites and host them on a shared server. One advantage would be that you will get improved search engine positions because a dedicated IP usually means a quicker loading site. Furthermore, you need such an IP when you intend to purchase an SSL certificate for your site and protect the info that visitors submit on it.