Hatching, in this sense, is a way of drawing or cutting: you lay down many thin parallel lines to make a shadow or to fill a shape. The lines sit side by side, like comb-teeth. When two sets of lines cross, that is cross-hatching, and the crossing makes the dark parts darker. Art teachers, printmakers, and map-makers use this word; the surface can be paper, metal, or wood. Though actually, English has another hatching that students meet first: a baby bird or fish coming out of an egg. That is just the verb hatch with -ing, and it is not this entry. Same spelling, two lives. This drawing sense comes from a different hatch, the one that means to mark with little cuts or lines. You will hear this hatching in art class and in printmaking, not on a farm.