All devices on the Web are recognized by a unique number called an IP address, such as 123.123.123.123. In case you have a website, the domain that you enter in order to open it is for your convenience, yet the server where your site files are still has an IP. Since there are a lot more sites and devices than there are IPs, all shared website hosting servers have a number of websites under the very same IP, while with a dedicated server you'll be given a dedicated IP too. Even in the first case though, you're able to get a dedicated IP for your sites and host them on a shared server. An advantage would be that you will have superior search engine positions because a dedicated IP generally means a faster loading website. Last but not least, you need such an IP if you would like to purchase an SSL certificate for your website and protect the info that visitors submit on it.
