Weltanschauung is a German word which literally means "looking onto the world," and is the origin of the English term "worldview," which was calqued directly from the German.
The term often appears in academic literature or the writings of people who want to seem erudite. It more or less means the same thing as "worldview", which would usually be a better choice if you want your reader to know what you are saying and not to think you are a pretentious ass.