World: Ambiguous term for the planet earth, reality, the universe, nature or a set of assumptions and practices that make one a member of some human society.
The last sense was introduced by the existentialists, with considerable justification, apart from the tenability of existentialism, because it is true that the human life most persons lead happens mostly in terms of assumptions and practices that make one a member of some human society.
Indeed, being a person involves - apart from madness, illness, sleep and unconsciousness - playing roles in human society.
Also, logic has contributed the notion of possible world: Whatever entities in one of various domains that satisfy some set of assumptions. This was introduced to consider various alternatives to what is so in fact: In another possible world you might have been taller, smarter, richer or perhaps not exist at all.