In U.S. land surveying under the Public Land Survey System (PLSS), a section is an area nominally one square mile, containing 640 acres (260 hectare, The hectare symbol ha is a metric unit of area defined as 10,000 square metres (100 m by 100 m), A hectare of land is about 2.47 acres). One of the reasons for creating sections of 640 acres was the ease of dividing into halves and quarters while still maintaining a whole number of acres. A section can be halved seven times in this way, down to a 5 acres (2.0 hectare) parcel, or half of a quarter-quarter-quarter section—an easily surveyed 50 square chain area. This system was of great practical value on the American frontier, where surveyors often had a shaky grasp of mathematics and were required to work quickly
Source; Wikipedia