The definition of a hero is
a. universally understood.
b. determined by personal and cultural factors.
c. clearly defined by a set of established traits.
d. static and impartial.

The definition of a Hero is actually more determined by personal and cultural factors B.

It would be hard to say that what a hero is is something that is understood universally given the fact that we have such a diversity in cultures. People often don't consider that what might be considered a heroic act in one culture, doesn't necessarily count as a heroic act in another culture. 

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