All devices on the Internet are identified by a unique number called an IP address, for example 184.108.40.206. In case you have a website, the domain name that you type in order to access it is for your convenience, yet the server where your website files are still has an IP. Considering that there are a lot more sites and devices than there're IP addresses, all shared hosting servers have a number of websites under an identical IP, whereas with a dedicated server you'll be given a dedicated IP too. Even in the first case though, you can acquire a dedicated IP for your sites and host them on a shared server. An advantage would be that you will get improved search engine positions as a dedicated IP usually means a faster loading site. In addition, you need such an IP when you want to purchase an SSL certificate for your website and shield the information that visitors submit on it.