All devices on the Internet are identified by a specific number called an IP address, such as 123.123.123.123. In case you have a website, the domain name that you enter to open it is to save you time, but the server where the website files are still has an IP address. Because there are many more websites and devices than there're IPs, all the shared web hosting servers have a number of websites under an identical IP, whereas with a dedicated server you will have a dedicated IP too. Even in the first case though, you'll be able to obtain a dedicated IP for your sites and host them on a shared server. One advantage would be that you'll get better search engine rankings because a dedicated IP generally means a quicker loading website. Furthermore, you need such an IP when you would like to purchase an SSL certificate for your website and secure the information that visitors submit on it.