All devices on the World Wide Web are recognized by a specific number called an IP address, such as 123.123.123.123. When you have a website, the domain name that you enter to open it is for your convenience, yet the server where the website files are still has an IP address. Since there are a lot more websites and devices than there're IPs, all shared web hosting servers have a number of sites under the same IP, while with a dedicated server you'll be given a dedicated IP too. Even in the first case though, you will be able to acquire a dedicated IP for your sites and host them on a shared server. An advantage would be that you will have superior search engine rankings because a dedicated IP generally means a faster loading site. Furthermore, you need such an IP if you intend to get an SSL certificate for your site and shield the data that your visitors submit on it.