A "chirp" is a signal whose frequency varies with time. The name comes from the "chirp" of a bird's call.
A practical example of a chirp is the "wee-woo" sound of emergency sirens; the sound is low in pitch at first, then gets higher in pitch, and then back down again.
What I did in "Chirp" is create a chirp with an initial and final frequency over a period of time.
Then, I multiplied that signal by a Gaussian to keep the ends of the signal near zero. Finally, instead of plotting the resulting function on a line, I made it into a circle by setting the radius at a given angle as the amplitude of the chirp.
To get the variety of shapes and colors, I randomly chose whether to blend, add, subtract, etc. each color from the underlying color when drawing the circle. In addition, I also varied the size and placement of the circle around a radius formed around the center of the image.