The bat'leth (tlhIngan Hol: betleH), or Sword of Honor, is the traditional weapon used by Klingon warriors and is the most used weapon throughout the Klingon Empire. The weapon is a crescent shaped blade with two bladed ends and consists of three handles which allow the warrior to wield it effectively. Baakonite is the preferred blade material composition of choice for a warrior. (DS9 episode: "Blood Oath") At the decree of Emperor Mur'Eq such weapons with blunted blades were introduced to ensure that warriors weren't killed while practicing with each other. (VOY episode: "Prophecy")
The creation of the bat'leth is almost mythical and was said to have been first forged by Kahless the Unforgettable. It was said that Kahless fashioned the first blade 1400 years ago by cutting a lock of his hair and dropping it into the Kris'tak volcano, after which he plunged the burning rock into Lake Lusor where he began to forge it into a weapon. This new blade, which later became known as the Sword of Kahless, was used to battle the hordes of the tyrant Molor. This prized possession of the Klingon people would be lost for many years during and after the Hur'q invasion of Qo'noS. (TNG episode: "Rightful Heir"; DS9 episode: "The Sword of Kahless"; DS9 reference: Star Trek: Deep Space Nine Technical Manual)
Until the appearance of Kahless, son of Kahless on Boreth, the story of the first bat'leth forged by Kahless was not widely known as it was a secret known only to a select few , including the Clerics of Boreth. The Clerics used the tale to determine if the true Kahless had returned by asking him details of the creation of the first bat'leth. Because the Clerics had programmed the memory of Kahless, the returned Kahless was able to correctly recite the story. After it was revealed that Kahless was a clone of the original, Kahless was installed as a ceremonial emperor. Following his installation, the story of the first bat'leth became widely known to the Klingon people. A holodeck simulation of the story was created, which Worf, Son of Mogh once observed. (TNG episode: "Rightful Heir"; TNG novel: Kahless)
Bat'leths were prized possessions of the Klingon people who would, usually, fight enemies in hand to hand combat with these blades. In Klingon society, Bat'leth competitions were held,which had warriors use their skill in the blade to best each other in combat.
A bat'leth was one the weapons created by (*) on the USS Enterprise as part of its efforts to provoke a conflict between the Enterprise crew and Klingons rescued from the IKS Voh'tahk. After the Enterprise crew and the Klingons refused to fight anymore, (*) left the Enterprise, leaving behind all the weapons it created. Lieutenant Hikaru Sulu kept the bat'leth and practiced with the weapon for many years, becoming proficient enough to engage the Albino in a bat'leth duel. (TOS episode: "Day of the Dove"; ST novel: Excelsior: Forged in Fire)
The Klingon word betleH originally meant "sword of honor" in an archaic dialect which was used in the time of Kahless the Unforgettable. In 24th century tlhIngan Hol, the same expression would be translated as batlh 'etlh, but this form is rarely used, except when explaining the etymology of the word betleH. (tlhIngan Hol reference: Klingon for the Galactic Traveler)