Such as ∞, the symbol for infinity. The class of such curves (as opposed to all the other figure-eight curves) is described by the equation r2 = 2a2cos(2θ) or, for those who don't think in polar coordinates, (x2 + y2)2 = a2(x2 - y2), where a is a parameter giving the distance of the curve's furthest point from the origin. First described by Jakob Bernoulli, one of the older generation of Bernoulli mathematicians. Named around 1780 -- apparently by Euler?, can't confirm this though -- from Latin lēmniscātus, adorned with ribbons, from lēmniscus, a pendent ribbon, from Greek lēmnískos, ribbon.
The skater traced a perfect lemniscate in the ice.