Acre
An acre was an old Earth unit of land area. Equivalent to 43,560 square feet or approximately 4,046 square Meters.

In 2267, Mr. Leslie reported to 
Captain James T. Kirk about his findings on Omicron Ceti III that "for an agricultural colony, they have actually very little acreage planted. There's enough to sustain the colony, but very little more." ()

In 2366, at a loss to understand how it was so, William T. Riker described the undamaged section of Rana IV as "a few acres of trees and grass and one building." ()

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Measurements