What is the real definition of a heroine?
The answer to this is really a combination of two questions: what does the word "heroine" mean, and what makes a person one?
To the first, there are 3 standard definitions I have found.
1. A woman admired for her courage, outstanding achievements, or noble qualities.
2. The chief female character in a book, play, or film, who is typically identified with good qualities, and with whom the reader is expected to sympathize.
3. A woman of superhuman qualities and often semi-divine origin, in particular one whose deeds were the subject of ancient Greek myths.
In modern (and geeky) society, we generally tend to use the second definition of which we are more familiar. Examples of these are women such as Wonder Woman, Xena, Catwoman and even Lara Croft. If we take the third definition which was taken from mythology and folklore, these characters fit the bill almost perfectly.
Let's take Xena for example. Her name was created from the ancient Greek word for stranger, "Xenos". As we know, she was originally a villain and a murderer but is defeated by Hercules and is redeemed. After this, she takes it upon herself to attone for these misdeeds by helping people in need and becoming a heroine in the process. I use the word heroine here as it meets the criteria for both the second and third definitions of the word.
What can make one a heroine is clear from the definitions: courageous, noble qualities, outstanding achievements. In other words, good qualities. In comic books, films and TV shows, a heroine is usually obvious with their need to do good and a lot of the time just by being a superhero (they don't get their name for nothing!). Xena however can be contradictory to this as she is attoning for her previous "black life" of murder, robbery and piracy and was even donned the "Destroyer of Nations".
In our modern day (and generally fairly boring) lives, a heroine can mean something entirely different than those in comic books. For us, the first definition is more appropriate and they are not always as easy to spot as heroines. Real life heroines do not don capes and masks, make themselves obvious with cool, spangly outfits or have super strength. Ours tend to just do good deeds without thinking of themselves as a heroine like Joan of Arc and Rosa Parks. They stand up for what they believe and never back down.