All devices on the World Wide Web are recognized by a unique number called an IP address, for example 188.8.131.52. When you have a website, the domain that you type to load it is to save you time, however the server where your website files are still has an IP address. Because there are a lot more sites and devices than there're IPs, all shared web hosting servers have a number of websites under an identical IP, while when you use a dedicated server you'll get 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 get superior search engine positions because a dedicated IP usually means a quicker loading website. Furthermore, you need such an IP if you want to purchase an SSL certificate for your site and secure the info that your visitors submit on it.