Looking up...
The world; the Earth and all its inhabitants.
El mundo es un lugar hermoso.
The world is a beautiful place.
A large or complex system or situation.
El mundo de la política es muy complicado.
The world of politics is very complicated.
Use 'mundo' to refer to the world in a general sense, and 'planeta' to refer to a specific planet.
From Old Spanish 'mundo', from Latin 'mundus', from Proto-Indo-European '*mei-'.
Commonly used in expressions like 'en todo el mundo' (all over the world) and 'el fin del mundo' (the end of the world).