Prelap is a screenwriting term That means clustering the dialogue from the next szene preceded the cut , and the Beginning of the dialogue is Heard in the outgoing stage. As an example:

 ADRIAN (VO, PRELAP)
 Peter? Peter, where are you?
EXT. THE WOODS -
Adrian DAY is out looking for Peter.
We see him wander around in the small forest.
 ADRIAN
 Peter? Hello? Are you there?

In this example, Adrian’s voice precedes the scene in the woods. The “VO” means ” Voice Over ” and the “PRELAP” indicates that Adrian’s dialogue should be heard before the next scene begins. Adrian, in this example, might not be in the scene when the prelap occurs. (“OS” or “Off Screen” would not be suitable for use in the field of unseen but on set.)

Prelaps can be of sound or dialogue, or anything non-visual, since a visual would indicate a direct cut to a new scene.