Cotton is one of the goods in Colonization. It can be grown on several different terrain tiles (see below), and can be woven into Cloth. A Master Cotton Planter increases Cotton yields. A Master Weaver increases Cloth production. A Weaver's shop or Textile mill also increases Cloth production.
Cotton is also a Bonus Resource which may be found on Prairies. Not surprisingly, it increases the production of Cotton (the good) on that tile.