All devices on the Web are identified by a special number called an IP address, such as 123.123.123.123. When you have a website, the domain name that you type to load it is for your convenience, but the server where the website files are still has an IP address. Because there're a lot more sites and devices than there're IP addresses, all shared website hosting servers have a number of sites under an identical IP, whereas using a dedicated server you will have a dedicated IP too. Even in the first case though, you're able to acquire a dedicated IP for your websites and host them on a shared server. An advantage would be that you'll get far better search engine positions as 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 website and shield the information that your visitors submit on it.