All devices on the World Wide Web are identified by a unique number called an IP address, for example 126.96.36.199. If you have a site, the domain name that you type in order to open it is for your convenience, however the server where the website files are still has an IP address. Due to the fact that there're far more sites and devices than there're IP addresses, all of the shared website hosting servers have a number of sites under the same IP, whereas when you use a dedicated server you'll get a dedicated IP as well. Even in the first case though, you will be able to get 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 because a dedicated IP usually means a faster loading website. Last but not least, you need such an IP when you intend to obtain an SSL certificate for your site and secure the information that your visitors submit on it.