This is a good question. We are fortunate, because the book defines courage for us. It is the commitment to do the right thing, even if you are going to lose. The person who personifies this type of courage is Atticus. He knows that his defending of Tom Robinson is not popular. He also knows that he is not going to win. However, he still commits to defending him with all of his heart.
Cowardice, on the other hand, is to do wrong, especially if it hurts other people. For example, Bob Ewell is the biggest coward in the book. He is the one who beats his daughter and he blames it on Tom Robinson, an innocent man. Moreover, when he felt disgraced by Atticus in a court of law, he went after his children, to kill them. This is the height of cowardice. He actually goes after children!
These two men are polar opposites. The former shows courage; the latter shows cowardice.
Courage and cowardice are two concepts examined throughout the novel. Atticus explains and defines what real courage is to Jem and Scout in Chapter 11. After Mrs. Dubose dies, Atticus tells his children that real courage is "when you know you're licked before you begin but you begin anyway and you see it through no matter what" (Lee 69). Atticus also demonstrates his courage by standing up to the mob outside of Tom Robinson's cell and defending Tom in court in front of a prejudiced jury. Other characters throughout the novel demonstrate courage through their actions. Toward the end of the novel, Boo Radley risks his life saving the children from Bob Ewell's attack.
Harper Lee examines cowardice throughout the novel by depicting Bob and Mayella Ewell. In a general sense, a coward is someone who allows fear to prevent them from doing what's right. To some degree, the majority of Maycomb's community might be considered cowards because they allow and encourage racial injustice; they allow fear of changes to the status quo and complacency to keep them from questioning the injustice they witness. The pressure to conform is powerful—but the moral wrong committed at Tom Robinson's trial is the greater evil by far.