Also known as a Paradigm, or Zeitgeist (for groups of people). Sometimes called a Map. In the Principia Discordia it's called a Grid.
It's the way you view the world, like through a lens.
If you see something that isn't in your model of the world, something so way out there, chances are that you will not see it right.
Like if you were to really see a zombie, you'd not understand that it's a zombie. Until it eats your brains, anyway -- then you'd have a Paradigm Shift.