An IP address is a unique number which distinguishes a website or a web server on the Internet, so if you have a dedicated IP, it'll be employed exclusively by your Internet sites and will not be shared with others as it happens with shared hosting accounts. In case you have your own server, you'll have a dedicated IP, but you may need extra ones for a variety of purposes. If you have an Internet store, for example, you will need an SSL certificate for it, to make sure that the payment info your clients submit shall be encrypted and secure. The same is valid in the event that 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 address, which should be different from the one that you already have on the hosting server. You could also need a separate IP for an application such as a VoIP server, or if you desire a slightly better overall performance for a given site, which shall affect its position in search engine results.