Under the historic Public Land Survey System, a quarter-section of land was often divided into forty-acre parcels. The north forty literally meant the northernmost forty acres of a property. Over time, it became a generic nickname for the most distant, hard-to-reach, or out-of-the-way field on any farm, regardless of its actual size or compass direction.
Heard on the job
Take the tractor out to the north forty and start clearing that brush before the rain hits.
Insider tip
Farmers frequently use this term as a joke for any far-off field, even if their total property is only ten acres.