Historical definition of Townland as the area that could be ploughed by a Seisreach (A Six-Horse team) in Forty Eight Days.  This is from Pádraig Ó Loingsigh history of the parish of Caherdaniel.

Old Irish Land Measurements Ploughlands and Gneeves frequently appear as land measurements in estate surveys, and deeds, leases, mortgages, marriage settlements up to the early 19th century.  From the time of the Ordnance survey adn Griffith’s Valuation 1850 they disappear.

In Gaelic society wealth was often computed by the number of cows a man had i.e. ‘Fear dhá bhó’ (a man of two cows).  There can be variation depending on soil fertility as as in Irish Féar dhá bhó, the grass of two cows, etc

Example of a deed:

1798, Richard Tonson Evanson, Mornhill, Co. Cork, and Nathaniel Evanson, Janeville, Co. Cork, eldest son of said Richard demise to William Swanton, Ballydehob, for various lives, part of the ploughland of Ardogoinagh lately in the occupation of William Justin and son to the westwards of the line of road from Carrigbui to Skibbereen, containing 9 Gneeves and the grazing of 13-14 collops at on the mountain of East Droumreiagh given to William Justin and son at a rent of £20 a year for 6 years and  thereafter.

 

From the book, “Census of Ireland, 1901: General Topographical Index…”, comes this explanation: “The Townlands and Baronies, which varied in different Provinces, are the most ancient divisions, and they existed under other names prior to the introduction of Christianity. The Barony or Trioca céad consisted of Ballybetaghs or Townlands, Ploughlands, Seisreaghs or Carrows, Tates or Ballyboes, Sessiaghs, Gneeves and Acres. The following is a Table showing these divisions: — 10 acres = 1 Gneeve. 2 Gneeves = 1 Sessiagh. 3 Sessiaghs = 1 Tate or Ballyboe. 2 Ballyboes = 1 Ploughland, Seisreagh or Carrow (120 aacres). 4 Ploughlands = 1 Ballybetagh or Townland 30 Ballybetaghs = 1 Trioca céad or Barony.

 

From Wikipedia:

collop (Irishcológ) is a measure of land sufficient to graze one cow. In Irish tradition, a collop is defined as the amount of land deemed capable of producing enough to support one family, or the number of cattle that the family could rear by pasture on it. It was the basis for the division of common land in the western parts of Ireland in the 18th and early 19th centuries. As in the Rundale system, the collop was scattered over several different fields, so that good and bad land was equally divided.[1] In Eric Cross’s The Tailor and Ansty, Timothy “the Tailor” Buckley describes a collop as “an old count for the carrying power of land”, noting that it was the grazing of one cow, or two yearling heifers, or six sheep, or twelve goats, or six geese and a gander, while a horse would require three collops. He describes it as a superior method of reckoning land to the acre, noting a man whose holding of 4,000 acres of barren land produces scarcely enough to feed four cattle.