An IP address is a unique number that separates an Internet site or a hosting server on the Internet, so in the event that you have a dedicated IP, it'll be used solely by your websites and won't be shared with other individuals as it happens with shared hosting accounts. If you have your own web server, you shall have a dedicated IP, but you may require extra ones for a variety of purposes. In case you have a web-based store, for example, you'll need an SSL certificate for it, to make sure that the payment info which your customers submit shall be encrypted and secure. The same is valid if you have a login form of some kind and you would like the usernames and the passwords that visitors enter 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 independent IP for an application such as a VoIP server, or if you want a slightly better efficiency for a given website, which may influence its position in search engine results.