The Joshua Project gives the following definition of an Unreached or Least-reached People Group:
“A people group among which there is no indigenous community of believing Christians with adequate numbers and resources to evangelize this people group.”
The original Joshua Project editorial committee selected the critieria less than 2% Evangelical Christian and less than 5% Christian Adherents. While these percentage figures are somewhat arbitrary, there are some that suggest that the percentage of a population needed to be influenced to impact the whole group is 2%. Joshua Project uses the terms Unreached People Group (UPG) and Least-reached People Group interchangably.