A concert performance or concert version is a performance of a musical theater or opera in concert form, without set design or costumes, and mostly without theatrical interaction between singers. Concert performances are commonly presented in concert halls without a theater stage, but occasionally also in opera houses when a scenic production is deemed too difficult or expensive. During a concert performance in an opera house, the orchestra does not play in the orchestra pit. Frequently, they play on the stage, with the choir (chorus) behind them and the soloists standing in front of them.