Opera is a dramatic form involving a performance set entirely to music with sung dialog. They are often performed in opera houses. Among the planets that have developed opera are Earth and Qo'noS.
The Doctor, USS Voyager's EMH, was particularly fond of this craft and added information and subroutines to his program to make him an opera singer. Due to this massive amount of info, his holographic matrix was in danger of destabilizing, but was ultimately repaired by merging it with the matrix of the EMH diagnostic program. (VOY: "The Swarm")
While patrolling the Romulan Neutral Zone in the USS Enterprise-E, during the Battle of Sector 001, captain Jean-Luc Picard listened to an opera by Berlioz. Commander Riker entered his office and mistook it for Bizet. (Star Trek: First Contact)
Kelemane's planet also developed opera. (VOY: "Blink of an Eye")