The symbol "∇²" represents the Laplacian operator, a mathematical tool used in various fields such as physics and engineering. It measures the rate at which a quantity changes in space, providing insights into phenomena like heat conduction and fluid flow. The Laplacian is often applied to functions defined in multiple dimensions. In mathematical terms, the Laplacian is the divergence of the gradient of a function. It can be expressed in Cartesian coordinates as the sum of the second partial derivatives with respect to each spatial variable. This operator is crucial in solving partial differential equations, such as those found in quantum mechanics and electromagnetism.