What is the 10/40 window and does it include Mexico

It doesn't, but it should in my opinion. https://am.adventistmission.org/mission-challenges

It stretches from North Africa, through the Middle East, and into East Asia, the 10/40 Window is home to more than two-thirds of the earth's population, many of the world's major religions, the largest and fastest-growing cities, some of the world's poorest people, and the fewest Christians. Many living within this region have never heard the name of Jesus.