This means that the constraints of the language parser affect the game reality, and what objects the game designer can use when constructing the world. In most text-based adventure games, you need to solve puzzle A before you move on to puzzle B, and so forth. There is a set sequence of problems, and usually only one or two ways to solve each problem. The constraints of the language guide the player into thinking in terms of specific actions without getting too caught up in fruitless endeavors. The rear deck of the house overlooks a field of ripening wheat, silvery-gold in the light of the full moon.
Moonlight ripples across the surface of a distant lake.
A two-person porch swing completes the romantic setting. There is a hoe on the top step of the porch. At first this seems like a strange response since the game obviously does understand the word moon, since it just used it in a description. But not allowing the parser to accept certain words, even if they had been used in description, was a conscious choice on the part of the game designer. In the previous example, the moon is superfluous to further progress in the game.