CERN is the world's largest particle physics laboratory, located in Geneva on the border of France and Switzerland. The letters stand for Conseil Européen pour la Recherche Nucléaire, French for European Council for Nuclear Research.
In the Flash Forward novel, an experiment at CERN is responsible for the Global Blackout.
In the FlashForward television series, the word "CERN" appears in orange on Dyson Frost's wall. ("The Garden of Forking Paths")