All devices on the Web are identified by a special number called an IP address, for example 188.8.131.52. When you have a site, the domain that you type to be able to access it is to save you time, yet the server where your site files are still has an IP. Because there are a lot more websites and devices than there're IP addresses, all the shared web hosting servers have a number of websites under an identical IP, whereas using a dedicated server you'll be given a dedicated IP as well. Even in the first case though, you'll be able to get a dedicated IP for your sites and host them on a shared server. An advantage would be that you may enjoy far better search engine positions because a dedicated IP often means a faster loading site. Also, you need such an IP when you plan to obtain an SSL certificate for your website and protect the info that your visitors submit on it.