totality of entities, to the whole of reality or to everything that is
When people say "the world" they usually mean Earth, especially in a cultural and geopolitical sense. Humans and all other known living things live in this world. Sometimes "world" means another planet.
Before people discovered that Earth is a planet, they often used "World" to mean "Universe". They still sometimes use it to mean all humans or all civilization. For example, they may say "end of the world" to mean the end of history or humanity.
Sometimes they mean a small part of Earth such as Western world, Islamic world, third world, new world, or ancient world.