\bigtriangleupThe symbol \bigtriangleup is used to represent the Laplace operator or the symmetric difference in set theory. It is also commonly used to denote a change or difference in a quantity, such as in physics or mathematics.
Symmetric difference of sets A and B
A \bigtriangleup BLaplace's equation in mathematics
\bigtriangleup f = 0Change in the variable x
\bigtriangleup x = x_2 - x_1