Neumann boundary condition

A Neumann boundary condition is when the value of a function at a boundary is related to the rate at which the function is changing at the boundary. Basically, it means that whatever is happening to one side of the boundary affects the other side. For example, if a fence is put up between two gardens, things that happen in one garden can still affect the other garden, like if one gardener waters their garden, the other may start to get wet too! Neumann boundary conditions help us understand how things on each side can interact.