Laplace operator
The Laplacian occurs in differential equations that describe many physical phenomena, such as electric and gravitational potentials, the diffusion equation for heat and fluid flow, wave propagation, and quantum mechanics.  The Laplacian represents the flux density of the gradient flow of a function.  For instance, the net rate at which a chemical dissolved in a fluid moves toward or away from some point is proportional to the Laplacian of the chemical concentration at that point; the resulting equation is the diffusion equation.  For these reasons, the Laplace operator is used in the sciences for modelling all kinds of physical phenomena. In image processing and computer vision, the Laplacian operator has been used for various tasks such as blob and edge detection.