An IP address is a unique number which identifies a website or a web server on the world-wide web, so if you have a dedicated IP, it will be used only by your sites and won't be shared with other people as it happens with shared website hosting accounts. If you have your own hosting server, you will have a dedicated IP, but you may require extra ones for various uses. In case you have an Internet store, for instance, you'll need an SSL certificate for it, so as to ensure that the payment information your clients submit shall be encrypted and protected. The same is valid if you have a login form of some type and you want the usernames and the passwords that visitors type in to be secured. The SSL certificate requires a dedicated IP address, which has to be different from the one which you already have on the hosting server. You may also need an independent IP for an application such as a VoIP server, or if you desire a slightly better overall performance for a given Internet site, which will affect its position in search engine results.