All devices on the Internet are recognized by a unique number called an IP address, for example 220.127.116.11. When you have a website, the domain that you enter in order to access it is to save you time, yet the server where the site files are still has an IP address. Considering that there're many more sites and devices than there're IP addresses, all the shared web hosting servers have a number of websites under an identical IP, whereas when you use a dedicated server you will have a dedicated IP too. Even in the first case though, you're able to get a dedicated IP for your websites and host them on a shared server. An advantage would be that you'll enjoy improved search engine positions as a dedicated IP often means a faster loading site. Furthermore, you need such an IP if you want to buy an SSL certificate for your website and secure the data that your visitors submit on it.