An IP address is a unique number that identifies a site or a web server on the world-wide web, so if you have a dedicated IP, it shall be employed only by your websites and won't be shared with other people as it happens with shared website hosting accounts. If you have your own web server, you'll have a dedicated IP, but you may require additional ones for many different purposes. In case you have an online store, for example, you'll need an SSL certificate for it, to make certain that the payment info which your clients submit shall be encrypted and safe. 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 secured. The SSL certificate requires a dedicated IP address, which ought to be different from the one that you already have on the web server. You may also need an individual IP for an app such as a VoIP server, or if you need a slightly better functionality for a particular website, which may affect its position in search engine results.