Curtilage is "the area to which extends the intimate activity associated with the 'sanctity of a man's home, and the privacies of life'" (Boyd v. United States, 1886). It is not necessarily enclosed by a fence. As a legal term, it's relevant for Fourth Amendment questions: a warrant and probable cause are needed to seize items in the curtilage. For example, trash left in the curtilage (not publicly accessible but where trash collectors are allowed to enter) is not considered abandoned; trash left outside the curtilage is considered abandoned and may be seized by police without a warrant.
In general, a locked gate and a 'no trespassing' sign do not make an open field part of the curtilage.
In use since the early 1300s, from Old French 'courtillage' (courtyard).
