(The following is taken from Joshua Project.)
The 10/40 Window is the rectangular area of North Africa, the Middle East and Asia approximately between 10 degrees north and 40 degrees north latitude. The 10/40 Window is often called "The Resistant Belt" and includes the majority of the world's Muslims, Hindus, and Buddhists. The original 10/40 Window included only countries with at least 50% of their land mass within 10 and 40 degrees north latitude. The revised 10/40 Window includes several additional countries that are close to 10 or 40 degrees north latitude and have high concentrations of unreached peoples.
Approximately 5.22 billion individuals residing in 8,883 distinct people groups are in the revised 10/40 Window. 6,169 (69.4%) of these people groups are considered unreached and have a population of 3.16 billion. This means approximately 61% of the individuals in the 10/40 Window live in an unreached people group. The 10/40 Window is home to some of the largest unreached people groups in the world such as the Shaikh, Yadava, Turks, Moroccan Arabs, Pashtun, Jat and Burmese.