I found this on Wikipedia.com
Debeaking, also called beak trimming is the partial removal of the beak of poultry, especially chickens and turkeys. Most commonly, the beak is shortened permanently, although regrowth can occur. The trimmed lower beak is somewhat longer than the upper beak. USA's UEP guidelines suggest that in egg laying strains of chickens, the length of the upper beak distal from the nostrils which remains following trimming, should be 2 to 3 mm[1]. The term debeaking implies that the entire beak is removed during the trimming process, though in reality only half or less of the beak is removed
In some countries, such as the United States, beak trimming is common in egg-laying strains of chickens and turkeys as a preventive measure to reduce the incidence of cannibalism and improve livability.[3] However, commercial broiler chickens are not routinely beak trimmed due to their docile nature. In some countries, beak trimming is done as a last resort where alternatives are considered not to be possible or appropriate.