Photo of a bottle house in Sultana, CA from Matt (mister Goleta)’s Flickr Photostream
In mathematics, a self-similar object is exactly or approximately similar to a part of itself (i.e. the whole has the same shape as one or more of the parts). Many objects in the real world, such as coastlines, are statistically self-similar: parts of them show the same statistical properties at many scales. Self-similarity is a typical property of fractals.
Wikipedia entry on self-similarity