Klingon opera was a well-known genre of traditional Klingon music with certain dramatic and stylistic similarities to Human opera. Typical themes included passionate tales of doomed courage and star-crossed love. Its strident tones were considered ear-shattering by most non-Klingons.
One famous Klingon opera singer was Barak-Kadan, while a noted opera writer was Keedera. Worf was an aficionado of Klingon opera and owned a sizable collection, which he often played at high volume over the USS Defiant speakers. (DS9: "Looking for par'Mach in All the Wrong Places", "In the Cards")
Odo mentioned Klingon opera in 2369, in a hypothetical situation as to why he had never dated anyone. He told Quark that a compromise could lead to someone "spending an agonizing night listening to Klingon opera". (DS9: "A Man Alone")
Klingon opera is a required subject of study in Federation secondary schools. In 2370, Jake Sisko had an exam on Klingon opera. Although he was confident, Benjamin Sisko believed he would not gain an "appreciation" of it by not studying it throughly. His father would later admit that he has not listened to Klingon opera for years. (DS9: "The Alternate")
After Worf and Elim Garak went into the Gamma Quadrant in 2373, searching for Enabran Tain, Jadzia Dax looked after Worf's opera collection. The Klingon was worried that Dax might lose them, Jadzia told him to "hurry back... if you want to keep your collection intact". (DS9: "In Purgatory's Shadow")
In order to get two meters of electro-plasma conduit from the Defiant later that year, Nog listened to Worf's operas at eighty-two decibels to filter out sub-harmonic distortions. (DS9: "In the Cards")
When The Doctor prevented several USS Voyager crewmembers from sleeping in sickbay by keeping it lightened, Neelix told him they'd then make a sing-along, including a Vulcan funeral dirge, some Talaxian rondos and the classics of Klingon opera; the Doctor then conceded. (VOY: "Demon")
Although he was extremely shy about it, Worf enjoyed singing along when he listened to Klingon opera. He was stranded for some time in an escape pod in 2375, and he found the acoustics in the pod conducive to sound. Despite Worf's claim that he had not sung while in the escape pod, Ezri guessed that he had been singing Shevok'tah gish. Reluctantly, he admitted he had been singing Gav'ot toh'va. Ezri noted that it had some ambitious solo passages. (DS9: "Penumbra")