tau
Tau is the ratio constant of a circle's circumference to radius, equal to 2 * pi, approximately 6.2832.
Try it yourself:
$1  tau
 
$2  2 * pi

See also:
All constantsTau is the ratio constant of a circle's circumference to radius, equal to 2 * pi, approximately 6.2832.
Try it yourself:
$1  tau
 
$2  2 * pi
