All devices on the Internet are identified by a special number called an IP address, such as 188.8.131.52. In case you have a website, the domain
that you enter to access it is for your convenience, but the server where the website files are still has an IP. Due to the fact that there are many more sites and devices than there're IPs, all of the shared website hosting servers have a number of websites under an identical IP, whereas using a dedicated server you'll have a dedicated IP as well. Even in the first case though, you can obtain a dedicated IP for your sites and host them on a shared server. An advantage would be that you may enjoy better search engine rankings since a dedicated IP usually means a quicker loading website. Last but not least, you need such an IP if you intend to purchase an SSL certificate for your website and secure the information that visitors submit on it.