The singular support of a generalized function 
is the complement
of the largest open set on which 
agrees with a C∞
function. Roughly speaking, it is the closed set
where the generalized function does not correspond
to a C∞ function.
Singular Support
See also
Fourier Transform, Generalized Function, Sheaf Singular Support, SupportThis entry contributed by Todd Rowland
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References
Folland, G. B. Introduction to Partial Differential Equations, 2nd ed. Princeton, NJ: Princeton University Press, 1995.Referenced on Wolfram|Alpha
Singular SupportCite this as:
Weisstein, Eric W., with contributions by Todd Rowland. "Singular Support." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/SingularSupport.html