The "Gameplay" category describes the main objects of the game, the function of the objects and their main purpose in the actual game; along with how they connect to the other parts of Godville.
It's truly impossible to be on a quest and never run into a monster. The hero will fight monsters (almost always) as soon as they encounter them. Hence the descriptions of monsters would go into the "Monsters" category.
And there are more categories, but you can visit those on the wiki.