All devices on the Internet are recognized by a specific number called an IP address, for example 188.8.131.52. When you have a website, the domain name that you enter in order to open it is for your convenience, however the server where the website files are still has an IP. Due to the fact that there are many more websites and devices than there're IP addresses, all shared hosting servers have a number of websites under the same IP, whereas using a dedicated server you'll be given a dedicated IP too. Even in the first case though, you are able to get a dedicated IP for your websites and host them on a shared server. An advantage would be that you'll enjoy better search engine positions since a dedicated IP generally means a faster loading website. Furthermore, you need such an IP in case you intend to buy an SSL certificate for your site and shield the info that visitors submit on it.