Selion is a mediaeval open strip of land or small field

Field (agriculture)

In agriculture, the word field refers generally to an area of land enclosed or otherwise and used for agricultural purposes such as:* Cultivating crops* Usage as a paddock or, generally, an enclosure of livestock...

 used for growing crop

Crop

Crop may refer to:* Crop, a plant grown and harvested for agricultural use* Crop , part of the alimentary tract of some animals* Crop , a modified whip used in horseback riding or disciplining humans...

s, usually owned by or rented to peasants. A selion of land was typically one furlong

Furlong

A furlong is a measure of distance in imperial units and U.S. customary units equal to one-eighth of a mile, equivalent to 220 yards, 660 feet, 40 rods, or 10 chains. The exact value of the furlong varies slightly among English-speaking countries....

 (660 ft) long and one chain (66 ft) wide. However, exact measurements could vary depending on geography of the land. The area of one furlong by one chain is one acre

Acre

The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. The most common use of the acre is to measure tracts of land.The acre is related...

. Monasteries or similar institutions were often bequeathed selions and then derived an income

Income

Income is the consumption and savings opportunity gained by an entity within a specified time frame, which is generally expressed in monetary terms. However, for households and individuals, "income is the sum of all the wages, salaries, profits, interests payments, rents and other forms of earnings...

from them by letting.