Energy whip

From Memory Alpha, the free Star Trek reference

The energy whip is a hand-held weapon used by the Ferengi. When lashed, it fires a pulse of energy that stuns the target.

The Ferengi marauder Ulis, who attempted to raid the Earth starship Enterprise in 2151, was armed with an energy whip. (ENT: "Acquisition")

The Ferengi landing party encountered by a USS Enterprise-D away team in the Delphi Ardu system in 2364 were also armed with energy whips. (TNG: "The Last Outpost")

Marauder Mo, a line of Ferengi action figures, usually had a toy energy whip as an accessory. (DS9: "Ferengi Love Songs")

[edit] Background information

Along with the fur sash, the energy whip was envisioned as a staple of the Ferengi ensemble. However, the producers felt both contributed to the unintended "silliness" of the Ferengi, and dropped both after the first season of Star Trek: The Next Generation in favor of more militaristic uniforms and weapons. (Star Trek Universe)