where the meaning
is contained not in the aesthetics
of the piece
but in its effect
on the viewer
through their interaction
with the piece.
Classic example: an installation where the patrons file through a dim corridor toward a brilliant gallery, only to stumble on a cement block embedded in the floor at the doorway, and, presumably cursing and rubbing their toes, look around to find the gallery empty.
The intended effect is an oscillation in the patrons' minds between annoyance at the trap, bewilderment at the lack of obvious Art in the room, and delight at the realization that the art was not in the room but in them, and between themselves and the artist, who at that very moment might be asleep somewhere, under a parasol.