The Mandelbrot set is a set of complex numbers. It is defined as all complex numbers c for which the recurrence relation z_n+1 = (z_n)^2+c does not grow to infinty. A visualization of the Mandelbrot set can be created by plotting the real and imaginary components of each constituent complex number along the x and y axes.
The Mandelbrot picture below is a Scalable Vector Graphic (SVG), not a raster image. Fractals are costly to render using SVGs because each point in the fractal must be represented by an SVG element. I tried to esacape this problem by grouping contiguous points into single-element blocks, thus greatly reducing the total amount of markup required. Clicking on each block will load a zoomed image of the points in that block, perhaps revealing details hidden at the previous resolution.