Prowling generally refers to the crime of lurking in an area with an intent to commit a crime. Laws governing prowling vary by state, so local laws should be consulted for applicability in your area.
The following is an example of a state law dealing with prowling:
§61.30. Loitering or Prowling; Defined & Punished; Defenses. (a) A person commits a violation if he loiters or prowls in a place, at a time, or in a manner not usual for law-abiding individuals under circumstances that warrant alarm for the safety of persons or property in the vicinity. Among the circumstances which may be considered in determining whether such alarm is warranted is the fact that the person takes flight upon appearance of a peace officer, refuses to identify himself, or manifestly endeavors to conceal himself or any object. (b) Unless flight by the person or other circumstances makes it impracticable, a peace officer shall prior to any arrest for an offense under this Section afford the person an opportunity to dispel any alarm which would otherwise be warranted, by requesting him to identify himself and explain his presence and conduct. (c) No person shall be convicted of an offense under this Section if the peace officer did not comply with Subsection (b) or if it appears at trial that the explanation given by the person was true and, if believed by the peace officer at the time, would have dispelled the alarm.