The "HistoricalDocuments" is the name given by the aliens
in GalaxyQuest to the episodes of the program by the same
More specifically: Within the context of the film, the aliens received television broadcasts of the original GalaxyQuest TV show, and assumed that they were real. They were so inspired by the ideals of GalaxyQuest that they built their entire civilization around the TV show.
The aliens then refer to the original broadcasts as the "HistoricalDocuments."
The whole concept of "Historical Documents" is an endemic problem in software development, as the UsualWayOfDoingThings has spawned many HistoricalDocuments which are followed blindly, regardless of their actual value to the process.
See also OldRulesWithForgottenReasons