An archetype refers to a prototype after which other things are modelled. In literature, it refers to a character that represents a universal or well-known pattern of behaviour. Common archetypes are villains, heroes, damsels in distress and mentors.
The sheriff of Nottingham is an example of an archetype, as he demonstrates all the obvious characteristics of "villains." He is the main antagonist in the legend of Robin Hood. The sheriff is a tyrant, who mistreats the local people. He has no respect for justice and no concern for human suffering. He is ambitious, and values money and status above else. These are all well-known characteristics of typical villains.