An IP address is a unique number that separates a site or a hosting server on the Internet, so in the event that you have a dedicated IP, it will be used just by your Internet sites and won't be shared with other people as it happens with shared website hosting accounts. In case you have your own hosting server, you'll have a dedicated IP, but you may need extra ones for many different uses. In case you have an electronic store, for example, you shall need an SSL certificate for it, in order to ensure that the payment information that your customers submit shall be encrypted and safe. The same is valid in the event that you have a login form of some kind and you wish the usernames and the passwords which visitors input to be protected. The SSL certificate requires a dedicated IP address, which has to be different from the one which you already have on the hosting server. You could also need an individual IP for an app such as a VoIP server, or if you desire a slightly better efficiency for a particular site, which will influence its position in search engine results.