Final answer:
The book 'The Gray Ghost' read by Atticus is a metaphor for Boo Radley's life, symbolizing the misjudgment and misunderstanding Boo faces in his community.
Step-by-step explanation:
The book Atticus chooses to read, The Gray Ghost, is a metaphor for the life of Boo Radley. A metaphor is a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable. In this context, Atticus reading The Gray Ghost represents a deeper layer of meaning about Boo's character and his life, suggesting that Boo, like the character in the book, is misunderstood and wrongfully judged by those around him.