Opera seria
Opera seria was often called dramma per musica ("drama through music").  The story was told in recitative, a quick-flowing music with simple accompaniment.  Then there were arias which were the big songs where the singers could show off their skills.  They were normally in da capo form (a main section, a middle section, and the main section repeated).  The opera would start with an overture and there would also be some ensembles where several characters sang at once.