Some one please tell me difinition of "Impartial Jury." I tried to find it, but couldn't get it.

Question

Law professors have agonized over that for hundreds of years. In the US, case law focuses on the jury must represent the cross section of the population, and that they are willing to judge based on the evidence.

See:
http://caselaw.lp.findlaw.com/data/constitution/amendment06/05.html

Thank you so much