A threshing board is an obsolete farm implement used to separate cereals from their straw; that is, to thresh. It is a thick board, made with a variety of slats, with a shape between rectangular and trapezoidal, with the frontal part somewhat narrower and curved upward (like a sled or sledge) and whose bottom is covered with lithic flakes or razor-like metal blades.

One form, once common in the Mediterranean Sea area, was "about three to four feet wide and six feet deep (these dimensions often vary, however), consisting of two or three wooden planks assembled to one another, of more than four inches wide, in which several hard and cutting flints crammed into the bottom part pull along over the grains. In the rear part there is a large ring nailed, that is used to tie the rope that pulls it and to which two horses are usually harnessed; and a person, sitting on the threshing board, drives it in circles over the cereal that is spread on the threshing floor. Should the person need more weight, he need only put some big stones over it."

The dimensions of threshing boards varied. In Spain, they could be up to approximately two metres in length and a metre and a half wide. There were also smaller threshing boards, as little about a metre-and-a-half long and a metre wide. The thickness of the slats of the threshing board is some five or six centimeters. Nonetheless, since threshing boards are nowadays custom made, made to order or made smaller as an adornment or souvenir, they may range from miniatures up to the sizes previously described.

The threshing board has been traditionally pulled by mules or by oxen over the grains spread on the threshing floor. As it was moved in circles over the harvest that was spread, the stone chips or blades cut the straw and the ear of wheat (which remained between the threshing board and the pebbles on the ground), thus separating the seed without damaging it. The threshed grain was then gathered and set to be cleaned by some means of winnowing.