I don't think I had a good working definition of "Courage" until I had children. When my twins were probably around 2 or 3, Girl1 was afraid of something or other. I can't remember specifically what it was, but I do remember that she was willing to try whatever it was that scared her despite that fear. I remember telling her, "Being brave doesn't mean you're not afraid. It means that you ARE afraid, but you're willing to try anyway." I then pointed out that she showed real courage in facing her fears.
I've used that definition quite a bit with all the kids. When my son insists, "I can't. I'm afraid," I have a two-fold answer for him. First off, my children are repeatedly told that there's nothing they can't do without help. Instead of, "I can't," they say, "I need help," or "I don't know if I can, but I'll try." Secondly, I remind him that it's okay to be afraid, but asking for help and trying shows courage. "I know you're afraid. I know you can be brave too."