A fractal is a geometric figure which is self-similar. Sounds very complicated and it actually is. A fractal has an infinite number of details and in some fractals there are all kinds of small figures that appear in those details to infinity. In addition, there is a fractal dimension that is used because the dimensions of many fractals cannot be properly captured in one (a line), two (e.g. a square) or three (e.g. a cube). Instead, fractals often move into dimensions that are in between numbers. The one-and-a-half dimension, for example. Complicated, isn't it? And hard to imagine. For an example, Google the Mandelbrot set.