An IP address is a unique number that distinguishes a site or a server on the Internet, so if you have a dedicated IP, it'll be used just by your sites and will not be shared with other individuals as it happens with shared web hosting accounts. Provided you have your own hosting server, you'll have a dedicated IP, but you may need additional ones for many different purposes. If you have an electronic store, for instance, you will need an SSL certificate for it, in order to make sure that the payment information that your clients submit shall be encrypted and protected. The same is valid in the event that you have a login form of some type and you wish 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 that you already have on the machine. You may also need a separate IP for an app such as a VoIP server, or if you would like a slightly better efficiency for a particular website, which may influence its position in search engine results.