Atticus tells Scout that rape is carnal knowledge of a female without her consent.
The trial of Tom Robinson is a rape trial. Robinson was accused to raping a white woman, Mayella Ewell. Scout is a little young to know about sex, let alone rape. She asks Calpurnia what rape is, and Cal tells her that she has to ask her father.
Scout does ask Atticus, and she does not understand his definition.
He sighed, and said rape was carnal knowledge of a female by force and without consent.
“Well if that’s all it is why did Calpurnia dry me up when I asked her what it was?” (Ch. 14)
Scout has no idea what “carnal knowledge of a female” means, and probably does not understand the concept of consent. "Carnal knowledge" means sex, and "consent" means the woman’s permission. Atticus gave Scout a very wordy definition of forcing a woman to have sex, although rape is more like a man forcing himself on a woman. It was an evasive answer.
Atticus is usually a pretty honest parent, and explains even difficult concepts to his children. The definition he gave is interesting, because he had earlier told Jack not to be evasive in answering a child’s questions. Jack told Atticus that Scout asked him what a whore-lady was. Atticus asked Jack if he told her the truth.
“No, I told her about Lord Melbourne.”
“Jack! When a child asks you something, answer him, for goodness’ sake. But don’t make a production of it. Children are children, but they can spot an evasion quicker than adults, and evasion simply muddles ‘em. …” (Ch. 9)
Atticus did not follow his own advice in answering Scout’s question about rape. Perhaps he decided that she simply was not ready for the answer, and it was okay for her to be muddled a little while longer.
The issue of children hearing about rape comes up again at the trial. There is a request for women and children to leave, but Judge Taylor does not grant it. He basically says that people who brought their children to a rape trial should have known what was going to be discussed.