What is Ranger?

Legal Definition
In forest law. A sworn officer of the forest, whose office chiefly consists in three points: To walk daily through his charge to see, hear, and inquire as well of trespasses as trespassers in his bailiwick; to drive the beasts of the forest, both of venery and chace, out of the deafforested into the forested lands; and to present all trespassers of the forest at the next courts holden for the forest. Cowell.
-- Black's Law Dictionary