Definition of back forty in English:

back forty

noun

United States Regional, North
Canadian
  • An (undefined) acreage of usually uncultivated land forming the remotest part of a farm, ranch, etc.

Origin

1930s; earliest use found in American Home. From back + forty. Also written with numerical symbol for the second element.

Pronunciation

back forty

/ˌbak ˈfɔːti/