Which term refers to the audience's seating just below stage level?

The term that refers to the audience's seating just below stage level is "Stalls." This seating area is located on the main floor of the theatre, typically at a lower elevation, and allows for a close-up view of the performances. The stalls often provide a more immersive experience as the audience is positioned directly in front of the stage, enhancing the visual and auditory engagement with the performance.

In contrast, the other options refer to different seating arrangements within a theatre. The balcony is positioned high above the main floor, offering a bird's-eye view, while the orchestra, although sometimes used interchangeably with stalls, generally refers to seating specifically designated for musicians, especially in musical performances. The mezzanine is typically a partially raised seating area that is positioned above the main floor but not as high as the balcony, further differentiating it from the stalls.