The mathematical constant that is the circumference of a circle divided by its radius, equal to twice pi.Some have suggested that pi is the wrong choice of constant to describe the geometry of circles etc. and tau = 2*pi would have been better. Most practising mathematicians think this is silly. The xkcd comic strip facetiously proposed a compromise of 1.5*pi or "pau". The Pi Manifesto.
Last updated: 2013-12-10