Fractal is a term used to describe a shape that reveals more and more structure the future one zooms in to it.
Sometimes the structure revealed resembles the overall shape at a smaller scale.
The term fractal refers to fractional dimension. For example a shape's boundary might be a line that zig and zags more and more intricately the closer it is examined. There is a sense in which this line is no longer one dimensional but has a fractal dimension between 1 and 2.
