(historical) An outlying part of a forest, exempted from forest laws and returned to private owners.
Origin of purlieu
Middle English purlewepiece of land on the edge of a forestprobably alteration (influenced by Old French lieuplace) ofporale, puraleroyal perambulationfrom Old French poralefromporalerto traversepor-forth (from Latin prō-pro–1) aler, allerto goalley1
American Heritage Dictionary of the English Language, 5th Edition
Land which had thus been once forest land and was afterwards disafforested was known as purlieu - derived by Manwood from the French pur and lieu, i.e.
The forest laws still applied in a modified manner to the purlieu.
The benefit of the disafforestment existed only for the owner of the lands; as to all other persons the land was forest still, and the king's wild beasts were to "have free recourse therein and safe return to the forest, without any hurt or destruction other than by the owners of the lands in the purlieu where they shall be found, and that only to hunt and chase them back again towards the forest without any forestalling" (Manwood, On the Forest Laws - article "Purlieu") .