Supernetting, also known as Classless InterDomain Routing (CIDR), is another awesome subject. It exists thanks to the wide adoption of the Internet, which lead to the exhaustion of the available IP Addresses. More specifically, supernetting was invented in 1993 with the purpose of extending the 32 bit IP address lifetime until the adoption of IPv6 was complete.
Putting it as simply as possible, supernets are used to combine multiple Class C networks into groups, which the router, in turn, treats as one big network. It might not seem like a smart thing to do, but if you look at the picture on a larger scale you will notice some of the really awesome advantages this offers.
The creation of Supernets is also known as Address Aggregation.
The sections below analyse Supernetting and CIDR, both which are extremely important to understand since they are used by all ISP's and large networks.