Simplify the following text for a Grade 9 native English-speaking person.
Original: Italian opera seria ( invariably to Italian librettos ) was produced not only in Italy but also in Habsburg Austria , England , Saxony and other German states , even in Spain , and other countries . Opera seria was less popular in France , where the national genre of French opera was preferred .
Simplified: Opera seria is an Italian term which refers to the `` serious '' style of Italian opera in the 18th century .