A whip was a device with a long slack end used as a punishment or a goad.
In 1893, Samuel Clemens asked the buggy driver to take him to the Presidio and not to spare the whip. (TNG: "Time's Arrow, Part II")
In 2267, after Khan Noonien Singh called the war to end tyranny "an attempt to unify humanity" Spock compared it to "a team of animals under one whip". (TOS: "Space Seed")
In 2268, James T. Kirk was impressed by Kloog's prowess with his whip while fighting against him. (TOS: "The Gamesters of Triskelion") Later that year, upon attempting to enter to quarters of Dohlman Elaan, Kirk was told by a guard outside that "the Dohlman has promised I'll be whipped to death if I let Captain Kirk pass through that door." (TOS: "Elaan of Troyius")
Whips were used by the Romulan guards in the Remus Dilithium mines. (Star Trek Nemesis)