What does "heroism" mean?

Heroism: The qualities characteristic of a hero, as courage, bravery, fortitude, unselfishness, etc.; the display of such qualities. Heroism is the self-devotion of genius manifesting itself in action. Hare. Courage is generic, denoting fearlessness or defiance of danger; fortitude is passive courage, the habit of bearing up nobly under trials, danger, and sufferings; bravery is courage displayed in daring acts; valor is courage in battle or other conflicts with living opponents; intrepidity is firm courage, which shrinks not amid the most appalling dangers; gallantry is adventurous courage, dashing into the thickest of the fight. Heroism may call into exercise all these modifications of courage. It is a contempt of danger, not from ignorance or inconsiderate levity, but from a noble devotion to some great cause, and a just confidence of being able to meet danger in the spirit of such a cause. Cf. Courage.