All devices on the Internet are identified by a unique number called an IP address, for instance 123.123.123.123. In case you have a website, the domain name that you type in order to access it is for your convenience, however the server where the website files are still has an IP address. Due to the fact that there are a lot more sites and devices than there are IPs, all of the shared web hosting servers have a number of websites under an identical IP, while when you use a dedicated server you'll have a dedicated IP as well. Even in the first case though, you're able to get a dedicated IP for your websites and host them on a shared server. One advantage would be that you may enjoy better search engine rankings because a dedicated IP generally means a faster loading website. What is more, you need such an IP in case you would like to obtain an SSL certificate for your site and protect the data that visitors submit on it.