Section (land)
In U.S land measure, a section is an area nominally one mile square, containing 640 acres. Nominally, 36 sections make up a township.Some sections vary slightly in size to compensate for the fact that the Earth is round. These unusually sized sections are placed at the westernmost or easternmost edges of some townships.
The legal description of a tract of land in the parts of the United States that use this system includes the name of the state, name of the county, township number, range number, section number, and portion of a section. Sections are customarily surveyed in halves and quarters, and further subdivision in halves and quarters is common. A quarter quarter section is 40 acres, and is the smallest unit of agricultural land commonly surveyed.
The phrases "front 40" and "back 40," referring to fields of crops on a farm, refer to quarter quarter sections.