Crosswind
Wind that blows across the line of fire, the component that pushes a bullet sideways the most and forces the largest windage correction at long range.
A crosswind blows perpendicular to the direction you are shooting, which makes it the most punishing wind a long range shooter faces. The full-value component of any wind, the part acting at a right angle to the bullet’s path, is what drives lateral drift, so a pure 90-degree wind delivers the maximum sideways push for a given speed. This is why reading the wind value of a flag or mirage matters as much as reading the raw speed.
To hit center you have to offset for that drift, either by holding into the wind with the reticle or by adding windage on the turret. A wind that shifts back and forth across the line, called a fishtail wind, keeps the value changing shot to shot, which is part of why honest wind reading is the hardest skill in the discipline.