 What do the characters refer to as "the world?"
The Sense of Wonder By MILTON LESSER Illustrated by HARRY ROSENBAUM When nobody aboard ship remembers where it's going, how can they tell when it has arrived? Every day for a week now, Rikud had come to the viewport to watch the great changeless sweep of space. But ever since the engines somewhere in the rear of the world had changed their tone, from the steady whining Rikud had heard all twenty-five years of his life, to the sullen roar that came to his ears now, the feelings had grown. The stars—it was a meaningless concept to Rikud, but that was what everyone called the bright pinpoints of light on the black backdrop in the viewport—were not apparent in the speckled profusion Rikud had always known. Instead, there was more of the blackness, and one very bright star set apart by itself in the middle of the viewport. But something soft had cushioned the impact—something which had come into being just for the moment and then abruptly passed into non-being again, something which was as impalpable as air. A long time ago the reading machine in the library had told him of the elders—a meaningless term—who had governed the world. There had been a revolt—again a term without any real meaning, a term that could have no reality outside of the reading machine—and the elders were overthrown. The people had decided that they did not know where they were going, or why, and that it was unfair that the elders alone had this authority. They were born and they lived and they died as the elders directed, like little cogs in a great machine. Much of this Rikud could not understand, but he knew enough to realize that the reading machine had sided with the people against the elders, and it said the people had won. Rikud often thought of his own death, still seventy-five years in the future, not without a sense of alarm. True, this was the only case of its kind, the exception to the rule, but it proved the world was not perfect. You can find several of them under 'astronomy,' with a cross-reference under 'stars.' "You know," Rikud said, sitting up now, "the stars in the viewport are changing." "Astronomy says some stars are variable," Crifer offered, but Rikud knew his lame-footed companion understood the word no better than he did.
 Their ship, which is all they have ever known.
 Their ship, which is all they have ever known.  The men's quarters, which is all they have ever known.  The planet they are preparing to plummet onto.  They use it as a general term for the "universe."