Widow's Bite are gauntlets used by Black Widow as her primary weapon for combat.
Iron Man 2
When the Chitauri attacked New York, Black Widow uses the Black Widow's Bite to electrocute several army of Chitauri. Also use it to electrocute a French pirate when she was aboard the Lemurian Star.
Romanoff used again the Widow's Bite to attack the Winter Soldier and destroy the bomb attached to her by Alexander Pierce, allowing Fury to kill Pierce.
In Avengers Assemble, Black Widow can shoot an electric pulse from her gauntlets. Her gauntlet in the show has not been given a name, but is seemingly based off the gauntlet shown in the films.