It's when a party A is about to inadvertently cause a disaster,
which is obvious to a second party, B, who is powerless to prevent it. The consequences of the disaster may befall on either party A or B, or a third party C.
In 'Dramatic Irony', party B is the audience.
( ,
Sat 10 May 2008, 21:25,
archived)
In 'Dramatic Irony', party B is the audience.