Civilization. Tech Tree. Technology or technologies (or Advances in the early civ games) are what you research to further advance your empire to enable the use of new units, buildings, wonders, or other powers.
For a complete list look at the specific technology tree for your game. Civilization Civilization II Civilization III.
Fan Sites. Comprehensive Civilization-Related. CivFanatics. CIVILOPEDIA Online. October 15, 2013 - Updated all languages for game version 188.8.131.52 September 12, 2013 - Added missing Game Info section to Terrains and Features where applicable August 23, 2013 - Updated all languages for game version 184.108.40.206 July 18, 2013 - Corrected images for Promotions.
Gods & Kings version is still available here but will no longer be updated. July 9, 2013 - Updated for Brave New World Expansion July 3, 2013 - Updated all languages for game version 220.127.116.11 November 20, 2012 - Updated all languages for game version 18.104.22.168 November 4, 2012 - Fixed missing Korean text November 1, 2012 - Updated all languages for game version 22.214.171.124. Wiki.