This was the term used by a group of musicians who attempted bring in elements of opera, particularly Wagnerian opera into Rock music. They seemed to have been active in the 1980's but it apparently never had much commercial success. Rather a pity because one of the two songs released by Fire Inc. is a classic. Never heard of them? well listen to this.
The recording does not do it justice but that is the best available. Their other song is worth listening to as well.
Of course there were other musicians like Meatloaf and Queen who were influenced by opera, whether they fall into this school I do not know.
These are some of my favourites:
I'd do anything for love
Rock´N´Roll Dreams Come Through
ps. There is another oldie that is rather good, its not operatic rock but the song is good. Albert Hammond's The Free Electric Band