All 4 Uses of

opera
in
Flora & Ulysses

...someone was singing. It was opera.
p. 115.2 *

opera = a song from a classical music play in which most of the dialogue is sung

Opera music.
p. 115.2

opera = a musical play with orchestra in which most of the dialogue is sung (or the art form that consists of such musicals; or describing something as related to that art form)

The opera music was very loud now Flora looked down at the hand that was on her arm.
p. 116.2

Definitions:

(1) (opera)
a musical play with orchestra in which most dialogue is sung -- (typically associated with classical music and often in a language foreign to the audience)

or:

the art form (or describing something as related to it) that consists of musical plays with orchestra in which most dialogue is sung
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Less commonly, the expression, soap opera, refers to a television or radio program that typically runs for many years and dramatizes the lives of a group of characters.