A fourier series is a way of representing some arbitrary function as a sum of lots of sine and cosine waves.
The above example is a visualisation of a square wave approximation. We can represent this as a point following the path of a circle at some speed (one sine/cosine wave), and another circle with associated point starting at the previous and so on and so forth. This illustrates the summation of a series of sine/cosine waves with varying frequencies. The fourier series for a square wave is as follows: Σ ∞n=1,3,5...(1/n)sin(nπx). Each one of these summation terms are represented as a circle.
