Zeitgeist comes from two German words: zeit, which means time, and geist, which means spirit. Together they refer to the spirit of the times, a prevailing mindset or attitude, even a set of values.
An example of zeitgeist would be how the world responded after WWII. Grief and relief. Exhaustion with hope. Time for a new beginning.
An example of how zeitgeist can be manipulated and steered would be the post WWII governments of the world and the popular media of each prospective nation. Suspicions and espionage. Threats of nuclear war instead of nuclear energy. The Iron Curtain vs. Capitalist Imperialism.
Art, science, medicine, education, architecture and technology are all influenced by this social force. It is a comprehensive way of describing why we do what we do, when we do it.
I like to think of zeitgeist as the tide of civilization. It carries a populace to a destination: gently washing ashore a sandy beach, or crashing into the rocks. I hope for the former and not the latter.
Regardless of where we end up, storms will occur. Ride'm!