All devices on the Internet are identified by a specific number called an IP address, such as 123.123.123.123. When you have a website, the domain that you type in order to access it is to save you time, yet the server where the site files are still has an IP. As there are a lot more websites and devices than there're IPs, all the shared website hosting servers have a number of websites under an identical IP, whereas when you use a dedicated server you will have a dedicated IP as well. Even in the first case though, you can get a dedicated IP for your sites and host them on a shared server. One benefit would be that you'll have far better search engine rankings as a dedicated IP generally means a quicker loading website. What's more, you need such an IP in case you want to buy an SSL certificate for your site and secure the information that visitors submit on it.