Definition
To thoroughly observe or examine a place, in order to familiarize oneself with its workings in preparation for criminal activity, often robbery.
To thoroughly observe or examine a place, without any nefarious motive or intent.
How People Actually Use It
To visit a house, store, or other establishment, with intent to burglarize or rob it later. Usually involves locating cameras and other security devices, and planning out one's exact course of action for the heist.
"To the security guards, he looked like an ordinary tourist; little did they know he was actually there to case the joint."
Source: Urban Dictionary