An IP address is a unique number that identifies an Internet site or a server on the world-wide web, so if you have a dedicated IP, it shall be used solely by your Internet sites and shall not be shared with others as it happens with shared website hosting accounts. Provided you have your own web server, you will have a dedicated IP, but you may need extra ones for a variety of purposes. In case you have an electronic store, for instance, you'll need an SSL certificate for it, in order to make sure that the payment info that your customers submit shall be encrypted and secure. 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 input to be secured. The SSL certificate requires a dedicated IP address, which has to be different from the one that you already have on the server. You might also need an individual IP for an application such as a VoIP server, or if you want a slightly better overall performance for a given site, which may influence its position in search engine results.