What is a section in the rectangular survey system and how large is it?

A section is a one-mile-square parcel of land containing 640 acres within the rectangular survey system. Each township contains 36 sections numbered in a serpentine pattern starting with section one in the northeast corner and ending with section 36 in the southeast corner. Sections can be subdivided into halves of 320 acres, quarters of 160 acres, and smaller fractions. Section 16 was historically reserved for school funding in many states.