What was a three-dimensional world? What was a two-dimensional world?

The concept of three-dimensional world and two-dimensional world was often used to describe the virtual world in fictional works. The three-dimensional world usually refers to the three-dimensional space of the real world, which is the virtual world corresponding to the real world we are in. In the two-dimensional world, it usually refers to a virtual world composed of characters and scenes on a two-dimensional plane. The characters usually have the characteristics of the two-dimensional characters such as height, appearance, etc., while the scenes are usually based on two-dimensional animation, comics, games, and other works. It should be noted that the concept of the two-dimensional world and the three-dimensional world being fictional did not exist in the real world. In fictional works, the two-dimensional world and the three-dimensional world could be different story backgrounds and spaces, and the characters and scenes could exist in different worlds according to their own settings.