The concept is simple caring for others until they can care for themselves. Prayer and financial support of cross-cultural missions is invested in the teaching of the Gospel and the planting of national churches. People groups are most commonly described in terms of ethnolinguistic peoples. This means that they share a common language and ethnic background. Least-reached peoples, sometimes called hidden peoples, are those people groups among whom there is no viable community of believers able to evangelize its own, apart from outside assistance.
Outside assistance comes in the form of cross-cultural missions.
The idea of people-group thinking is not a new one. It was discussed at the 1947 Lausanne I Conference as a vital principle for world church growth. But its history goes back much further and transcends eternity. The Psalmist wrote, Declare his glory among the nations, his marvelous deeds among all peoples. It also provides a means by which we may finish the task the establishment of a vibrant national church among every people group on the earth.