All devices on the Internet are recognized by a unique number called an IP address, for instance 184.108.40.206. When you have a website, the domain name that you type to access it is for your convenience, but the server where your website files are still has an IP address. Due to the fact that there are a lot more websites and devices than there are IPs, all of the shared website hosting servers have a number of websites under the same IP, whereas with a dedicated server you'll have a dedicated IP too. Even in the first case though, you will be able to acquire a dedicated IP for your sites and host them on a shared server. An advantage would be that you may enjoy improved search engine positions because a dedicated IP generally means a faster loading site. Also, you need such an IP when you would like to acquire an SSL certificate for your site and shield the data that visitors submit on it.