An IP address is a unique number which distinguishes a site or a hosting server on the Internet, so if you have a dedicated IP, it shall be used exclusively by your websites and shall not be shared with other individuals as it happens with shared hosting accounts. If you have your own hosting server, you will have a dedicated IP, but you may need extra ones for many different purposes. Provided you have an online store, for instance, you shall need an SSL certificate for it, to make certain that the payment info your clients submit will 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 that visitors type in to be protected. The SSL certificate requires a dedicated IP address, which should be different from the one that you already have on the hosting server. You might also need an individual IP for an application such as a VoIP server, or if you would like a slightly better performance for a particular Internet site, which will affect its position in search engine results.