A binary operator representing symmetric difference of sets or upward-pointing triangle in set theory and logic.
Examples
Forward difference operator in discrete mathematics
\bigtriangleup f(x) = f(x + 1) - f(x)
Laplace operator in vector calculus
\bigtriangleup f = \frac{\partial^2 f}{\partial x^2} + \frac{\partial^2 f}{\partial y^2} + \frac{\partial^2 f}{\partial z^2}
Change in a quantity
\bigtriangleup x = x_2 - x_1