Question

The idea that even if something is out of sight, it still exists is called ________.

Answer 1

The idea that even if something is out of sight, it still exists is called object permanence.
This is something that is developed in humans over time - young children still don't have the notion of object permanence. This is why peekaboo games work well with children - because when you hide your face, the child doesn't know it is still there behind your hands because there is no concept of object permanence yet.