(performing arts, idiomatic) The imaginary invisible wall at the front of the stage in a proscenium theatre, through which the audience sees the action in the world of the play.

(idiomatic) A quiet, non-participating, or unseen observer; an eavesdropper or witness.

(idiomatic, jargon) An information barrier within an organization, designed to ensure internal confidentiality; frequently used to prevent conflicts of interest.

A brick wall, having enclosed flues connected to a fire, to which fruit trees are attached in order to hasten growth and ripening

Used other than figuratively or idiomatically: see brick, wall. A wall made of bricks. / (figuratively) An obstacle. / (sound engineering) A type of anti-aliasing filter with a steep cutoff.

To build a brick wall around. / (sound engineering) To filter using a brick wall filter. / To halt or limit abruptly. / To be uncooperative and unresponsive.

Any of several structures used to restrain a vertical-faced mass of earth.

(idiomatic) crazy, mad

(idiomatic, UK, Ireland, regarding a workplace, etc.) Very busy, swamped.

plural of brick wall