A variant form of the uppercase Greek letter Gamma commonly used to represent special functions or function spaces in analysis.
Examples
Gamma function notation
\varGamma(n) = (n-1)! \text{ for positive integers } n
Boundary of a domain in multivariable calculus
\oint_{\varGamma} F \cdot dr = \iint_D (\nabla \times F) \cdot n\,dS
Graph theory vertex set notation
\text{The vertex set } \varGamma(v) \text{ denotes the neighbors of vertex } v