Nickname for any sniper rifle from the Gears of War series, Or the Halo series. The name comes from the first Gears of War where the sniper rifle somewhat resembled a windshield wiper.
Hence the name Sniper Wiper. Can also be implied when someone that is god like with the sniper picks it up and commences to "wipe" out the whole enemy team.
Hes got the sniper wiper! Stop him!