An IP address is a unique number which identifies a website or a server on the Internet, so if you have a dedicated IP, it will be employed solely by your websites and will not be shared with others as it happens with shared hosting accounts. Provided you have your own server, you shall have a dedicated IP, but you may require additional ones for various purposes. Provided you have an online store, for instance, you shall need an SSL certificate for it, to ensure that the payment info that your clients submit will be encrypted and protected. 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 secured. The SSL certificate requires a dedicated IP, which has to be different from the one that you already have on the hosting server. You might also need an independent IP for an app such as a VoIP server, or if you would like a slightly better performance for a given site, which will influence its position in search engine results.