The lemniscate of Bernoulli, here by aklego, is a plane curve defined from two given points F1 and F2, known as foci, at distance 2a from each other as the locus of points P so that PF1·PF2 = a2. This is a special case of a Cassini oval (which is simply where the product of the two distances equals a constant).
BTW, all of that description came straight from Wikipedia. It's been a lot of years since I took a formal math class, and don't remember these at all.
