code - the three letters the cm puts into the computer to tell it which deal you are getting if other than rack rate...think of other hotel/airline/rental car ressies online where there is a place to enter the discount code you might have.
Pin - the set of numbers that allows you to access a Pin Code.
Pin Code - a code that is only accessible by a Pin
PostCard/Email - Disney's method of Letting you know you have a Pin for a Pin Code. It contains information about the deal and the Pin but does not actually contain the Pin Code.
Think of the "deal" as your bank account. Your bank account is identified by an account number (the code, in this case the Pin Code). To access this account from an atm (think CM or online system) you need your Pin number (Pin).
Apparently the public isn't given the Pin Code since giving the Pin automatically accessess the Pin Code.