Histories of the English forest inevitably use Fitz Nigel's definition of the forest from his Dialogus de Scaccario of Henry II's reign as their reference point. In their supplement to Stubbs's Constitutional History on English forests, Ch. Petit-Dutaillis and Georges LeFebvre went so far as say that ‘the nature of the Forest could not be more clearly stated’, and H. A. Cronne wrote that there is ‘no more succinct definition of the Forest’.

Fitz Nigel's definition stresses three things: legal structures, royal hunting, and royal prerogative. He believed that noble love of the hunt was the only reason for the forests’ existence. Because scholars have tended to follow the lead of Fitz Nigel and similar legal texts, almost all histories of the English forest discuss it primarily as a royal hunting ground with its own legal system.

While Fitz Nigel specifically mentioned beasts that live in woods as important to forests, we must remember from the outset that forest as a medieval term is not synonymous with the modern usage of the word to mean woodland; forest could include many kinds of land, including pasturage, heath, and even farmed land. The medieval forest in England did not imply continuous tree-cover, although many forests were well wooded. By the thirteenth century, designated forests in England encompassed wooded lands such as the forests of Dean and Hants, but Dartmoor and Exmoor, for example, were moorland, and still others, such as Sherwood, were heath. The origin of the word forest is obscure.