An IP address is a unique number which separates a site or a web server on the Internet, so in the event that you have a dedicated IP, it will be used only by your websites and will not be shared with others as it happens with shared hosting accounts. Provided you have your own hosting server, you will have a dedicated IP, but you may require additional ones for many different purposes. If you have an online store, for example, you shall need an SSL certificate for it, in order to make certain that the payment information that your customers submit will be encrypted and safe. The same is valid in case you have a login form of some sort and you wish the usernames and the passwords that visitors type in to be protected. The SSL certificate requires a dedicated IP, which should be different from the one which you already have on the web server. You might also need an individual IP for an app such as a VoIP server, or if you would like a slightly better efficiency for a given Internet site, which will affect its position in search engine results.