All devices on the Web are identified by a unique number called an IP address, for example 188.8.131.52. When you have a website, the domain name that you type to be able to open it is for your convenience, but the server where the site files are still has an IP address. Due to the fact that there are many more websites and devices than there are IP addresses, all of the shared website hosting servers have a number of websites under an identical IP, while with a dedicated server you will have a dedicated IP too. 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 have better search engine rankings because a dedicated IP often means a faster loading site. Furthermore, you need such an IP in case you want to purchase an SSL certificate for your site and protect the data that your visitors submit on it.