An opera is a stage work written for virtuoso singers as soloists, and a chorus, who also act on the stage. They are backed by a full orchestra. The word derives from
Latin 'opus' whose plural is 'opera', thus meaning 'works'. In most early and traditional operas there is no spoken dialogue, everything is sung. The conversational or declarative sections are called 'recitative' as they are recited, often in a montone. A song is called an 'aria', which is Italian for 'air'. Many of these are written to display the virtouso talents of the lead singers. The leading lady is usually a soprano and is called the 'prima donna'. Another term frequently used to describe a prima donna is a 'diva', Italian for a 'goddess', but the leading man is never called a divo or dio (= 'god') because that would appear blasphemous..
Opera composers usually write an overture which is played at the beginning of the performance, before the curtain rises. Even though the orchestra is usually hidden in a 'pit' directly in front of, and below the stage, the overture is an important part of the opera, and well-behaved audiences listen attentively. Many composers have written operas which are long-forgotten, never performed on stage, but whose overtures live on in the concert hall. An excellent example of this is the 'William Tell' overture by Rossini.