The Observist Guide is a section of Star Citizen’s Galactapedia that integrates into the game's universe. RSI claims that it will "respond in real time as players steer the course of Star Citizen’s world." For example, if a player is the first to discover a new jump point, their name will be added to the Guide. The Guide will be available both in-game and on the RSI website.
While Chris Roberts mentioned wikis in his letter, it is currently unknown if any portion of the guide will be player editable.
The Guide can be accessed from the MobiGlas rig.
The Guide, along with the aforementioned rig, are $42 million stretch goals, and thus are currently will not be added into the game unless this goal is reached.