All devices on the Web are identified by a special number called an IP address, for example 123.123.123.123. In case you have a site, the domain name that you type to be able to access it is for your convenience, but the server where your site files are still has an IP address. Due to the fact that there're many 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 using a dedicated server you'll get a dedicated IP too. Even in the first case though, you are able to acquire a dedicated IP for your sites and host them on a shared server. One advantage would be that you'll get superior search engine positions as a dedicated IP often means a quicker loading website. Also, you need such an IP if you intend to purchase an SSL certificate for your website and secure the info that visitors submit on it.