A snapshot in time by week, month and year of what people were searching for in Google. Zeitgeist results were routinely published for the public beginning in 2001 but were dropped in 2007.
The vast knowledge Google accumulates about the interests of the human race, which is based on the millions of things people search for on Google. "Zeitgeist" is German for "spirit of the times" (Zeit = time; geist = ghost), and Google is said to know the Zeitgeist of the world better than any other organization. See big data