There are actually hidden and visible keys, hidden meaning they don't show up on your items page (these are like behind-the-scenes security stuff). An example of a hidden key would be the general boards key, which if taken away, you would lose access to most of the boards. In fact, new members don't get this key right away, which is why they can't access most boards.

Most keys are visible. There are 14 in all, some very exclusive. There is actually a key that only one person on the site has, and that person isn't Four Degreez!!

Visible keys:
Poetry Key
Activity Planning Key
Gold Premium Key
Silver Premium Key
Immigration Key(this is given to the members who approve members, not the new members themselves)
High Council Key

Invisible keys:
General Boards
Visa Key(which is for new members.)
Serf Key
Commoner Key
Bard Key
Alpha Key
Beta Key
Gamma Key