 What do the characters refer to as "the world?"
The Sense of Wonder By MILTON LESSER Illustrated by HARRY ROSENBAUM [Transcriber's Note: This etext was produced from Galaxy Science Fiction September 1951. 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. If he had understood the term, Rikud would have told himself this was odd. But it came again, and each time it left him with a feeling he could not explain. Rikud knew that something which he could not explain had entered the elder man's head for a moment, but it had departed almost before Chuls knew of its existence. A hardly perceptible purple glow pervaded the air in the room of the health-rays. Rikud, for his part, wanted to get back to the viewport and watch the one new bright star. Now why shouldn't a man be permitted to do what he wanted, when he wanted to do it? There was a strange thought, and Rikud's brain whirled once more down the tortuous course of half-formed questions and unsatisfactory answers. 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. Rikud had been stopped in this action, although there was no real authority to stop him.
 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."