world
The Italian word 'mondo' is used similarly to the English word 'world' - it can refer to the earth, the people on it, or a particular way of living or thinking. It can also be used in various expressions or phrases when directly translated.
The world is beautiful.
This is a straightforward declarative sentence expressing a positive opinion about the world, with 'mondo' as its subject.
I live in the world.
This sentence uses 'nel', which is a contraction of the preposition 'in' with the article 'il', before 'mondo' to mean 'in the world'.
The whole world knows it.
In this sentence, 'tutto il mondo' literally translates to 'all the world', but is often used to mean 'everyone' or 'everybody'.