Operas

Burlettas
Comic operas
Intermezzos (Operas)
Light operas
Opera buffas
Opera serias
Opéras comiques
Operettas
Puppet operas
Singspiels

Opera.

New Grove dict. of mus. WWW site, May 8, 2006: Intermezzo (term applied during the 18th century in place of the earlier Intermedio to a miniature comic opera in Italian (the French counterpart is the intermède) performed in segments between the acts of a larger work, usually an opera seria; flourished during the first half of the 18th century, then gradually disappeared, giving way to the fully-fledged comic opera)
New Harvard dict. of mus.: Comic opera (opera with humorous or lighthearted subject matter)
New Harvard dict. of mus.: Opéra comique (opera on a French text with musical numbers separated by spoken dialogue)
New Harvard dict. of mus.: Operetta (in the 17th and 18 centuries, an operatic work of small scale and pretensions that could equally well be classified as intermezzo, opera buffa, opéra comique, or Singspiel)
New Harvard dict. of mus.: Singspiel (musico-dramatic work with a German text, especially a work written in the 18th or early 19th century in which spoken dialogue alternates with songs and sometimes with ensembles, choruses, or more extended musical pieces)
Ewen, D. Book of European light opera, 1977 ("A guide to 167 European comic operas, light operas, operettas, opéra-comiques, opéra-bouffes, and opera buffas ...")
Encarta.msn.com dictionary WWW site, May 8, 2006: Opera seria 2 (Opera serias as a group)
New Grove dict. of mus. WWW site, Jul. 8, 2011: under Burletta (A type of English operatic comedy that flourished in the late 18th and early 19th centuries. The term was one of several used for Italian comic operas of the light intermezzo variety; early burlettas, in verse throughout and all-sung, satirized the mythological and historical conventions of opera seria, though the music rarely participated in the joke)

Here are entered musical compositions. General works about opera are entered under the heading