2. The first dimension is the word world, and the second dimension is the collective name of virtual products such as animation, games, comics and novels. In fact, the meaning of the word "secondary element" only represents the "flat world" and the "paper" world based on fantasy. The world view with two elements does not exist at all.
3. The third dimension is the real world relative to the second dimension.
4. Different dimensions refer to parallel space, four dimensions, universe, etc.
Semantic evolution
The original meaning of the word "secondary element" is a two-dimensional plane and a concept of spatial dimension. Any point of the second dimension can be located by two coordinate axes (such as X axis and Y axis), and the area of the second dimension is usually expressed in 1 pixel.
The use of the word "secondary element" to refer to "overhead" originated in Japan, and now it is also used in Chinese circles outside Japan (the English word "fantasy" has similar meaning, but the word "fantasy" is not commonly used). For example, the early animation and comic works in Japan are all composed of two-dimensional images, and these images are a plane, so they are called "two-dimensional world" by animation lovers.
Referred to as "two yuan", the opposite is "three yuan", which is the real world. The ACGN cultural circle uses the word "secondary element" to mean "overhead", "imagination", "fantasy" and "fiction", and then refers to "overhead world".