What is Poaching?

Legal Definition
Poaching has traditionally been defined as the illegal capturing of wild animals, usually associated with land use rights.

According to Encyclopædia Britannica, poaching was performed by impoverished peasants for subsistence purposes and a supplement for meager diets. Poaching was as well set against the hunting privileges of nobility and territorial rulers. By contrast, stealing domestic animals (as in cattle raiding, for example) classifies as theft, not as poaching.

Since the 1980s, the term "poaching" has also referred to the illegal harvesting of wild plant species. In agricultural terms, the term 'poaching' is also applied to the loss of soils or grass sward by the damaging action of feet of livestock which can affect availability of productive land, water pollution through increased runoff and welfare issues for cattle.
-- Wikipedia
Legal Definition
In English criminal law. The unlawful entry upon land for the purpose of taking or destroying game; the taking or destruction of game upon another's land, usually committed at night. Steph. Grim. Law 119, et seq.; 2 Steph. Comm. 82.
-- Black's Law Dictionary
Legal Definition
Trespassing at night to kill game.
-- Ballentine's Law Dictionary