From the publisher:
It is the dawn of the sixth millennium and the skies are darkening, for the suns themselves are fading. Humans reached the stars long ago, building a Republic of high technology and universal emancipation--and then squandered it, fought over it, and finally lost it. A new Dark Age has descended on humanity, for the greatest of civilizations has fallen and even the stars die. Now, feudal lords rule the Known Worlds, vying for power with fanatic priests and scheming guilds.
from the FASA Games site
First Edition (FS1) is the original game created and published by Holistic Design, Inc. in 1996.
Second Edition (FS2) was published by Holistic Design, Inc. in 1999.
Second Edition Revised (FS2R) was published by RedBrick Limited (licensed from Holistic Design, Inc.) in 2007.
Revised Edition (FSR) is the current edition of Fading Suns, published by FASA Games, Inc. (licensed from Holistic Design, Inc.) in 2012.
Core Rulebooks contain everything necessary for players and Game Masters to play and run Fading Suns games.
Sourcebooks expand on information presented in the Core Rulebooks, dealing with specific aspects of the Fading Suns game.
Supplements contain pre-generated adventures, equipment, and less-specific information on Fading Suns.