An IP address is a unique number which identifies an Internet site or a server on the world-wide web, so if you have a dedicated IP, it will be used solely by your websites and won't be shared with other individuals as it happens with shared Internet hosting accounts. Provided you have your own hosting server, you'll have a dedicated IP, but you may need extra ones for many different purposes. In case you have an online store, for instance, you shall need an SSL certificate for it, so as to make sure that the payment information which your clients submit shall be encrypted and secure. The same is valid in case you have a login form of some kind and you want the usernames and the passwords which visitors enter 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 machine. You may also need an individual IP for an app such as a VoIP server, or if you want a slightly better efficiency for a certain site, which shall influence its position in search engine results.