The world is defined as the totality of entities, representing the whole of reality or everything that exists. Its nature has been conceptualized differently across various fields, with some conceptions viewing it as unique while others discuss a plurality of worlds. It is treated either as one simple object or as a complex made up of parts, serving as the fundamental scope for understanding existence and reality in philosophical and scientific contexts.

The English word world derives from the Old English weorold, which reflects the Common Germanic *weraldiz, meaning roughly 'age of man'. This etymology connects to mythological notions of a domain of man, opposed to divine or chthonic spheres. The Latin equivalent mundus expresses creation as establishing order out of chaos, while cosmogony studies the origin of the world and eschatology refers to the doctrine of its end, reflecting deep historical and linguistic roots.

In scientific cosmology, the world is commonly defined as the totality of all space and time, including all that is, has been, and will be. Theories of modality introduce possible worlds as complete and consistent ways things could have been, contrasting with the actual world. Phenomenology defines the world as the biggest horizon or the horizon of all horizons, incorporating relations between objects rather than just a spatiotemporal collection of them.

The term takes restricted meanings in various contexts, associated with Earth, humanity, or international scope. This includes world history, politics, religion, language, government, war, population, economy, and championships. In theology, the world is conceptualized in relation to God as creation or interdependent entity. Religions often downgrade the material world in favor of a spiritual one, with comprehensive representations known as worldviews guiding religious practice and understanding.

The concept encompasses diverse conceptions such as monism and pluralism, where existence monism states the world is the only concrete object. Priority monism allows other objects but holds they depend on the world. Scientific cosmology uses relativity to conceive space and time as a four-dimensional manifold called spacetime. Quantum cosmology conceives the whole world as one big wave function expressing particle probability, integrating mass into spacetime curvature.