The zeitgeist is the general feeling, mood, and set of ideas that belong to one period of time. Not what one person thinks — what seems to be 'in the air' for everyone. If you say the 1960s zeitgeist was one of change and freedom, you mean that this feeling was everywhere then: in the songs, in the clothes, in what young people argued about. The word almost always comes with 'the', and it almost always points at a time: the zeitgeist of the 1990s, the current zeitgeist, capture the zeitgeist. That last one is the most common thing people do with it — a film, a song, or a book 'captures the zeitgeist' when it says out loud what many people were already half-feeling. You will meet it in writing about culture, art, politics and news, and in serious talk. It sounds educated, and a little bit borrowed, because it is: people know it is a German word and enjoy using it. Two honest warnings, though. First, it is often used loosely, to mean not much more than 'what is popular right now' — a writer may say a new app 'fits the zeitgeist' when they really just mean lots of people like it. Careful users keep it for something bigger and slower than a trend: a shared way of thinking. Second, the whole idea is a guess. Nobody can measure the spirit of an age; we only decide afterwards what it was. So writers say 'the zeitgeist' with great confidence about a thing that is really an opinion.