What is a PNC?

Many people have heard of PNCs, but don't really know what it means even though they know what they are, a first day cover with a featured coin and stamp.  PNC is commonly know as Postal Numismatic Cover, or the correct term Philatelic Numismatic Cover.  These covers are usually produced by an official postal organisation in association with a mint, for example in Australia, Australia Post teams together with the Royal Australian Mint or Perth Mint, though there are a few private companies that produce them, for example Benham in the United Kingdom.  Australia Post would be one of the major producers of PNCs in the world, apart from the Royal Mail there are not many other major produces in the world.