All devices on the Internet are identified by a unique number called an IP address, for example 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, yet the server where your site files are still has an IP address. Considering that there're far more websites and devices than there're IP addresses, all of the shared website hosting servers have a number of sites under an identical IP, whereas with a dedicated server you'll get a dedicated IP too. Even in the first case though, you can get a dedicated IP for your sites and host them on a shared server. An advantage would be that you will have better search engine rankings because a dedicated IP generally means a quicker loading site. In addition, you need such an IP in case you intend to purchase an SSL certificate for your site and shield the data that visitors submit on it.