Ma and Jack like to play vocabulary games. It may seem like a childish thing to do, but it actually relies on great vocabulary skills. It shows that Jack knows a bunch of synonyms, and also that he understands that "huge" and "enormous" can be combined into one even bigger word.

Jack might understand a lot of words, but being trapped inside Room limits his ability to understand some of them. He thinks that he and Ma are the only "real" people and that everyone else, even the humans, inside the television are not real. It takes him a while to grasp this concept.

Because Jack only understands things (and people) he has seen in person, and because all his other knowledge comes from TV, he uses the word "TV" to mean "fantasy" or "imaginary." To Jack, anything that he hasn't laid his hands on is imaginary—even bunnies.