Wikipedia
The sabbath year (shmita , literally "release") also called the sabbatical year or shvi'it (, literally "seventh") is the seventh year of the seven-year agricultural cycle mandated by the Torah for the Land of Israel, and still observed in contemporary Judaism.
During shmita, the land is left to lie fallow and all agricultural activity, including plowing, planting, pruning and harvesting, is forbidden by halakha (Jewish law). Other cultivation techniques (such as watering, fertilizing, weeding, spraying, trimming and mowing) may be performed as a preventive measure only, not to improve the growth of trees or other plants. Additionally, any fruits which grow of their own accord are deemed hefker (ownerless) and may be picked by anyone. A variety of laws also apply to the sale, consumption and disposal of shmita produce. All debts, except those of foreigners, were to be remitted.
Chapter 25 of the Book of Leviticus promises bountiful harvests to those who observe the shmita, and describes its observance as a test of religious faith. There is little notice of the observance of this year in Biblical history and it appears to have been much neglected.