A function $u(x)$ of a point $x$ of a Euclidean space $\mathbf R^n$, $n\geq1$, or of a harmonic space such that $-u(x)$ is a subharmonic function.
A function that is both subharmonic and superharmonic is said to be a harmonic function.
Superharmonic function. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Superharmonic_function&oldid=31742