False Ground or Bootleg Ground
A false ground or bootleg ground involves using a jumper wire to connect the ground screw and the neutral screw on a receptacle. This is done to trick the hand held testers most inspectors use to check for open grounds.
This is a common trick used by misinformed do-it-yourselfers and some clueless handy men. The reason it is done is to disguise an ungrounded two wire electrical circuit and make it appear to be a grounded circuit.