Tosca was an opera written by Giacomo Puccini in the late 19th century on Earth.
Tosca was one of the operas being played at the Dorothy Chandler Pavilion in Los Angeles in 1996. (VOY: "Future's End, Part II")
When The Doctor viewed Tosca for the first time on the holodeck, he became very sad and sobbed throughout the third act. (VOY: "Imperfection")