All devices on the Web are identified by a special number called an IP address, such as 188.8.131.52. When you have a site, the domain name that you enter to load it is to save you time, yet the server where the site files are still has an IP address. Since there are many more sites and devices than there're IPs, all of the shared hosting servers have a number of sites under an identical IP, while using a dedicated server you'll have a dedicated IP too. Even in the first case though, you'll be able to acquire a dedicated IP for your websites and host them on a shared server. An advantage would be that you will enjoy better search engine positions as a dedicated IP often means a quicker loading website. Furthermore, you need such an IP if you plan to buy an SSL certificate for your website and secure the information that visitors submit on it.