What is fractal?

The word "fractal" was put forward in 1975 by B.Mandelbort, a researcher in the Department of Physics of IBM Research Center and a professor in the Department of Mathematics of Harvard University. Its original meaning is "an object with irregular fragments". 1977 published the first book "Fractal: Morphology, Contingency and Dimension"; After the birth of fractal theory, people began to realize that it should be used as a tool to study various topics in nature. Therefore, the application of fractal theory has made great progress. The theory and application of "fractal" cover a wide range, and the theory is very mathematical and professional, so it is omitted here.