A sign, a remark, or an image that anticipates something that will happen later in the work, sometimes only to those who reread it.
In One, No One, and One Hundred Thousand
A little later I had to climb back up to the Abbey to take from the corridor, under the big window, that revolver, which was afterward meant for me.
"Which was afterward meant for me" anticipates the shot that comes only in the Book's last chapter. The reader learns, ahead of time, that the object taken back without suspicion will be used against the narrator.