The symbol 
used to denote an integral 
. The symbol was invented by Leibniz and chosen to
be a stylized script "S" to stand for "summation."
Integral Sign
See also
Integral, Integration Under the Integral SignExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Integral Sign." From MathWorld--A Wolfram Web Resource. https://wwn.ikan3.com/7hz2929k26_9nqeuhigsnjcgsjpnuemse/IntegralSign.html