Orchestras also play with instrumental soloists in concertos. During concertos, the orchestra plays an accompaniment role to the soloist (e.g., a solo violinist or pianist) and, at times, introduces musical themes or interludes while the soloist is not playing. Orchestras also play during operas, ballets, some musical theatre works and some choral works (both sacred works such as Masses and secular works). In operas and ballets, the orchestra accompanies the singers and dancers, respectively, and plays overtures and interludes where the melodies played by the orchestra take centre stage.