All devices on the World Wide Web are recognized by a unique number called an IP address, for instance 188.8.131.52. In case you have a website, the domain that you enter in order to load it is for your convenience, but the server where the website files are still has an IP address. Considering that there are many more sites and devices than there are IPs, all shared web hosting servers have a number of websites under an identical IP, while 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 websites and host them on a shared server. An advantage would be that you'll get far better search engine rankings as a dedicated IP often means a faster loading website. Last but not least, you need such an IP when you would like to obtain an SSL certificate for your website and protect the data that your visitors submit on it.