Circs

Define: circle -  a closed plane curve consisting of all points at a given distance from a point within it called the center. Equation: x 2 + y2 = r2.

Wired has a new photo contest up for your best take on circles.  If you want to submit your own, or just check out the entries, check it out:
http://www.wired.com/culture/art/news/2009/02/submissions_circles