Night

We had already lived through a lot that night. We thought nothing could frighten us anymore. But his harsh words sent shivers through us. The word "chimney" here was not an abstraction; it floated in the air, mingled with the smoke. It was, perhaps, the only word that had a real meaning in this place. He left our barrack.

What is the meaning of "abstraction" as it is used in the passage above?