A standard Farmer's Best Friend model cattle prod produced by Wattz Electronics, the cattle prod is a metal pole with an electrically-charged coil wrapped around the end. Normally used for herding stubborn cattle, it has been re-purposed as a non-lethal weapon against humans.
The cattle prod is able to knock out enemies quickly because, in addition to lowering health, it causes fatigue damage. It is particularly useful against dangerous enemies because it knocks them out after a few blows. You can then attack their unconscious bodies at will.
It's special V.A.T.S. attack is "Lights Out", which does 125% damage at the cost of 36 action points (requires a Meleeskill of 50).