An IP address is a unique number that distinguishes a site or a web server on the Internet, so in the event that you have a dedicated IP, it will be used exclusively by your Internet sites and will not be shared with others as it happens with shared hosting accounts. In case you have your own server, you shall have a dedicated IP, but you may require additional ones for different uses. In case you have an online store, for instance, you will need an SSL certificate for it, so as to ensure that the payment info which your customers submit shall be encrypted and protected. The same is valid in case you have a login form of some kind and you would like the usernames and the passwords which visitors type in to be protected. The SSL certificate requires a dedicated IP, which needs to be different from the one which you already have on the web server. You may also need a separate IP for an application such as a VoIP server, or if you need a slightly better functionality for a given site, which shall affect its position in search engine results.