World space is the universal coordinate system used to track objects in the scene, as opposed to object space. When you look at the home grid in the viewports, you see the world-space coordinate system. World space is constant and immovable.
A book in object space rests on a table in world space.
All objects in your scene are located in world space by their position, rotation, and scale (their transforms).
Some modifiers operate in world space. See World-Space Modifiers (WSMs).
Space warps also operate in world space. A space warp defines an area in world space that is affected by the space warp’s parameters. Any object that is bound to the space warp is affected as it moves through the space warp’s area of world space.