PSC file

PSC file is a format used by Fallout games using the Creation Engine.

About
Source code file written in the Papyrus language; used to create a plugin for Fallout 4. Contains functions that define events that occur in the game, such as a message or the behavior of a character.

Once you create your PSC file, place it in the Data/​Scripts/​Source location in your installation directory. You can then compile the script and create a plugin by loading the appropriate .ESM file(s) in Creation Kit.