Facts are things the game remembers to decide what to do the next time a script (such as a quest) wants to look at past events in the game without directly looking up quest journal events. Basically, it is an unlocked cheat command. The developer console in The Witcher 3 is very similar to other dev consoles in games like Fallout 4 or Skyrim.
Devexpress excel export Dev Console Guide - DLC Item IDs List.