World From Top, By Klaus Lerdorf

'World' distinguishes the entire planet or population from any particular country or region: world affairs pertain not just to one place but to the whole world, and world history is a field of history that examines events from a global (rather than a national or a regional) perspective. Earth, on the other hand, refers to the planet as a physical entity, and distinguishes it from other planets and physical objects.
'World' can also be used attributively, to mean 'global', 'relating to the whole world', forming usages such as World community.
By extension, a 'world' may refer to any planet or heavenly body, especially when it is thought of as inhabited, especially in the context of science fiction or futurology.
'World', in original sense, when qualified, can also refer to a particular domain of human experience.