The Torah or Talmud uses two terms for a thief -- the "Gonif", (which is the more familiar term) and the "Gazlin", and two corresponding terms for robbery "Genaiva" and "Gezaila". What is the difference between the two?
A Gazlan is someone who steals openly (a robber), a Ganav is someone who steals quietly (a thief).
This well-sourced article proposes the logic behind Shmuel Brill's distinction. It concludes that a ganav is one who steals while concealed from view such that he deprives the owner of property without even an objection. The use of force that characterizes a gazlan is comparatively less serious a concern because in such an action no insulting presumptions are made by trying to maintain complicity or subterfuge; objections are simply rebuffed by the use of force. Thus subversive means of depriving people of their property are considered g'neva while blatant ones are considered gazlanus.