adj. taking place after death
v. to lay in the grave
n. a door
The principal trap in almost all theatres is known as the grave trap. This is one of the conventionalisms of the English stage, and is a testimony also the enduring influence of Shakespeare. It is well understood that at some time or another the play of ‘Hamlet’ will be performed in every theatre, and Ophelia‘s grave must therefore be dug in every stage — hence the grave trap. It may be that it is not always placed in the right position to suit the ideas of each new representative of the Royal Dane, and it has happened that it has been found too short for the reception of poor Ophelia‘s coffin; but it is never omitted in the construction of a stage.
— Folger Shakespeare Library Scrapbook, quoted in Paul Menzer, Anecdotal Shakespeare, 2015