A variant form of the capital Greek letter Delta commonly used to denote discriminants, differences, or Laplace operators.
Examples
Change in a variable
\varDelta x = x_2 - x_1
Discriminant in quadratic formula
\varDelta = b^2 - 4ac
Laplace operator in vector calculus
\varDelta f = \frac{\partial^2 f}{\partial x^2} + \frac{\partial^2 f}{\partial y^2} + \frac{\partial^2 f}{\partial z^2}