What Is 1D, 2D, 3D, And 4D In Barrel Racing?

Barrel Racing is a fairly well-known way of competition among horse racing enthusiasts. And often such competitions are held in 4D format (very rarely there is a 5D or 6D formats). And if you met with similar names, then you probably come across such designations as 1d, 2d, 3d, 4d. And in fact there is nothing supernatural, the answer lies on the surface.