Learn English – What do you call the floor-level space that allows someone to traverse from one floor to another with stairs

A key, or a token, depending on the context.

With the word key, I was referring to part of a machine component that is specially shaped to slot into, and lock with, the keyway of a shaft.

(Though, of course, a key more commonly refers to an object that slides in through the keyhole of a lock, and acts to unlock it.)

A token would be something similar to a coin, which would pass straight though a slot.

Perhaps hardcore gamer

Someone who plays video games as a primary hobby. They tend to spend large amounts of time playing games, often in excess of two or three hours a day.