All devices on the Internet are recognized by a specific number called an IP address, for example 123.123.123.123. In case you have a website, the domain name that you type to be able to load it is for your convenience, but the server where your website files are still has an IP. Considering that there are a lot more sites and devices than there're IPs, all the shared hosting servers have a number of websites under the very same IP, while when you use a dedicated server you will have a dedicated IP too. Even in the first case though, you can 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 positions as a dedicated IP usually means a faster loading website. Last but not least, you need such an IP in case you would like to purchase an SSL certificate for your site and shield the information that visitors submit on it.