A double integral operator used to calculate integrals over two-dimensional regions or surfaces in multivariable calculus.
Examples
Double integral over a rectangular region
\iint_{[0,1]\times[0,1]} x^2y \,dx\,dy
Double integral over a general region D
\iint_D \left(x^2 + y^2\right) \,dA
Double integral in polar coordinates
\iint_R r e^{-r^2} \,dr\,d\theta