Improvisation A situation in which the actors are provided with background on the setting and characters and then spontaneously invent dialogue and action.
Incidental Music Music written especially for a particular play and which seldom survives its production (as opposed to Broadway and Vaudeville tunes). Originated in Elizabethan English Theatre, but has been used in such modern productions as Tennessee Williams' Glass Menagerie and Truman Capote's Holiday Memories.
Inner Proscenium See, False Prosecenium. Structure, usually consisting of side flats with a transverse piece, that serves to temporarily reduce the opening of the permanent proscenium.
Interlude From the Latin interludium (between the play), the term refers to a short dramatic sketch in early English drama. The short, light pieces would be performed between the acts of more serious plays.
Italian Run-Through A rehearsal in which the actors deliver their lines and perform the action at a much higher rate of speed, usually trying to run the rehearsal at "double time". Used to help with the common problem of slow or dragging pacing. Once the actors have performed at the much faster pace, they often will not return to the problem pace of earlier rehearsals because the pacing will be slower only in relation to the faster pace of the Italian Run-Through. Also referred to as a "Russian Run-Through".