It's a notation for integrals, part of calculus. The "d" doesn't refer to anythi...

		rmc on April 9, 2012 \| parent \| context \| favorite \| on: What comes next: π/2, π/2, π/2, π/2, π/2, π/2, π/2... It's a notation for integrals, part of calculus. The "d" doesn't refer to anything http://en.wikipedia.org/wiki/Integral