Final answer:
Incidental music is designed to be performed during a play to enhance the emotional experience and set the mood, and it became particularly significant during the Romantic era.
Step-by-step explanation:
The type of romantic music specifically designed to be performed during a play is called incidental music. This genre is intended to accompany the action and dialogue on stage, enhancing the emotional experiences and setting the mood for the audience. Unlike opera, which is a fully sung dramatic work, or a symphonic poem which is a piece of orchestral music that illustrates a poem, story, or painting, incidental music serves as a background and is integrated into the flow of the theatrical performance itself.
During the Romantic era, composers like Brahms, Schumann, and Tchaikovsky, among others, expanded on the expressions of intense emotions in their music, which could be effectively employed within the context of plays as incidental music. The purpose of this music is to support the theatre's dramatic elements without overwhelming them, providing an enriching layer to the overall experience of the play.