What is Danelaw?

Legal Definition
The Danelaw (also known as the Danelagh; Old English: Dena lagunema; Danish: Danelagen), as recorded in the Anglo-Saxon Chronicle, is a historical name given to the part of England in which the laws of the Danes held sway and dominated those of the Anglo-Saxons. Danelaw contrasts West Saxon law and Mercian law.

Modern historians have extended the term to a geographical designation. The areas that constituted the Danelaw lie in northern and eastern England.

The Danelaw originated from the Viking expansion of the 9th century AD, although the term was not used to describe a geographic area until the 11th century AD. With the increase in population and productivity in Scandinavia, Viking warriors, having sought treasure and glory in the nearby British Isles, "proceeded to plough and support themselves", in the words of the Anglo-Saxon Chronicle for the year 876.

Danelaw can describe the set of legal terms and definitions created in the treaties between the West-Saxon king, Alfred the Great, and the Danish warlord, Guthrum, written following Guthrum's defeat at the Battle of Edington in 878. In 886, the Treaty of Alfred and Guthrum was formalised, defining the boundaries of their kingdoms, with provisions for peaceful relations between the English and the Vikings. The language spoken in England was also affected by this clash of cultures with the emergence of Anglo-Norse dialects.

The Danelaw roughly comprised 14 shires: York, Nottingham, Derby, Lincoln, Essex, Cambridge, Suffolk, Norfolk, Northampton, Huntingdon, Bedford, Hertford, Middlesex and Buckingham.
-- Wikipedia
Legal Definition
English law where the Danes had settled; that part of England once occupied by the Danes.
-- Ballentine's Law Dictionary