The American Jury

The Constitutional Rights Foundation Chicago has lesson plans on the history of juries as well as on JURY NULLIFICATION. 

DEFINITIONS - Jury Nullification

"Jury nullification occurs when guilt is established but the jury decides to acquit on its own sense of fairness, propriety, prejudice, or any other sentiment or concern." Randall Kennedy, Race, Crime, and the Law (1997) 

"Jury nullification… may take on a variety of meanings or shades of meaning." 

"True" or stringent nullification "occurs when the jury recognizes that a defendant's act is proscribed by the law but acquits because it does not believe the act should be proscribed. The behavior, in other words, is not criminal in the eyes of the jury." 

"Intermediate" nullification occurs when "although the act proved is properly classified as criminal, it is within a class of acts that do not deserve the punishment prescribed for them." 

"Weak" or "ad hoc" nullification "reflects the jury's view that although the act proved is criminal and falls in a class of acts that may well deserve the prescribed punishment, such punishment is inappropriate in the case at hand."