All devices on the Web are identified by a specific number called an IP address, for instance 220.127.116.11. In case you have a website, the domain name that you enter to open it is for your convenience, yet the server where the website files are still has an IP address. Since there're far more sites and devices than there are IP addresses, all the shared web hosting servers have a number of websites under the same IP, whereas when you use a dedicated server you'll get a dedicated IP too. Even in the first case though, you will be able to get a dedicated IP for your websites and host them on a shared server. An advantage would be that you will have improved search engine rankings because a dedicated IP generally means a quicker loading site. What's more, you need such an IP if you plan to purchase an SSL certificate for your site and protect the data that visitors submit on it.