Answer:
A mockingbird symbolizes innocence.
Explanation:
To kill a mockingbird is about the growing-up process of Scout Finch, a young girl from Alabama during the Great Depression.
There are two main events in the story, the first is the prosecution and trial of Tom Robinson, and the second is the murder (in self defense) of Bob Ewell.
During Robinson's unfair imprisonment which results in him being murdered, there is a final sentence that says that it is as unfair as killing a songbird.
At the same time, Scout and Jem are attacked by Bob Ewell and defended by Boo (the gloomy recluded neighbor) whose house they had trespassed before. Scout's innocence is in a sense 'murdered' when she witnesses Ewell's murder after the attack.
