All devices on the Internet are identified by a unique number called an IP address, for example 123.123.123.123. When you have a website, the domain that you enter in order to access it is for your convenience, yet the server where the website files are still has an IP address. Considering that there're a lot more websites and devices than there are IPs, all of the shared hosting servers have a number of websites under the very same IP, whereas 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. One advantage would be that you'll have improved search engine positions because a dedicated IP often means a quicker loading site. What is more, you need such an IP in case you want to acquire an SSL certificate for your website and protect the data that your visitors submit on it.