Hey so this might be a stupid question but what is post scratch pre scratch, scratch in general??

Pre-scratch is the timeline from before the Players’ initiated the Scratch (John and Meenah’s groups)

Post-scratch is the timeline from after they initiated the Scratch (Karkat and Roxy’s groups)

The Scratch is a game construct that rearranges where the Skaian Defense Portals go during the Reckoning, thus altering the timeline.