The house in a proscenium theatre refers to:

a
The seating area for the audience in the theatre, including the rows of seats facing the stage.
b
The area of the stage closest to the audience.
c
The offstage areas on either side of the stage, concealed from the audience's view.
d
The extended portion of the stage that projects towards the audience.

a

The seating area for the audience in the theatre, including the rows of seats facing the stage.