There are 40 acres in a parcel, which has four sides that measure 1,320 feet each. A square mile is 640 acres, with each side measuring 5,280 feet in length.
Beginning in 1832, the U.S. government parceled out land in 40-acre plots, also known as "quarter-quarter-sections." A section is 1 square mile, and 36 enumerated sections make up a township on a map. The term "40 acres and a mule" comes from this parcel concept.
In general, a parcel is a portion of something, such as a distinct tract of land. The term parcel goes back to the French term "parcele" from the 1400s.