Translation:What is opera? Is it when fat people sing?
After some research, I found that что такое is a fixed phrase meaning "what is", and it is indeclinable:
what is opera...this opera — что такое опера ... эта опера
what is love...this love — что такое любовь ... эта любовь
what is a bicycle...this bicycle — что такое велосипед ... этот велосипед
what are bicycles...these bicycles — что такое велосипеды ... эти велосипеды
what is an apple...this apple — что такое яблоко ... это яблоко
what are apples...these apples — что такое яблоки ... эти яблоки
As can be seen, it doesn't matter what gender or number is involved - although asking about plurals can possibly be a bit more complicated.
I actually sung this to the tune of DDT's "что такое осень"... https://www.youtube.com/watch?v=5KC-iscJtsI&ab_channel=navigator
Hey guys, I have no idea how long after your intial posts that I'm writing this. So, I'm not a native, but from what I understand, "Это" is not only the nom/acc form of "Этот" but ALSO can be used to simply mean "It is". And, in this instance, that appears to be the correct usage as "опера" is a feminine nominative noun, so it would have to be "Эта" (matching the noun's case and gender with the form of "этот") to produce a tranlsation, in this specific example, of "This is when" rather than "It is when".
In some senses of the word: "1. lacking sophistication or good taste; unrefined; 2. coarse and rude."
In American English, it also means "3. making explicit and offensive reference to sex or bodily functions" That doesn't fit.
I prefer the first two definitions, because they are he original sense of the word.