Opera (; English plural: operas; Italian plural: opere ) is an art form in which singers and musicians perform a dramatic work combining text (libretto) and musical score, usually in a theatrical setting. In traditional opera, singers do two types of singing: recitative, a speech-inflected style and arias, a more melodic style. Opera incorporates many of the elements of spoken theatre, such as acting, scenery, and costumes and sometimes includes dance. The performance is typically given in an opera house, accompanied by an orchestra or smaller musical ensemble, which since the early 1800s has been led by a conductor.

about is an internal URI scheme (also known as a “URL scheme” or, erroneously, “protocol”) implemented in various Web browsers to reveal internal state and built-in functions. It is an IANA officially registered scheme, and is standardized.

The Oscillation Project with Emulsion-tRacking Apparatus (OPERA) is an instrument used in a scientific experiment for detecting tau neutrinos from muon neutrino oscillations. The experiment is a collaboration between CERN in Geneva, Switzerland, and the Laboratori Nazionali del Gran Sasso (LNGS) in Gran Sasso, Italy and uses the CERN Neutrinos to Gran Sasso (CNGS) neutrino beam.

Todmobile is an Icelandic pop/rock band which was very popular in Iceland in the 1990s.