In vector calculus, the divergence's an operator that measures the magnitude of a vector field's source or sink at a given point; the divergence of a vector field's a (signed) scalar. For example, consider air as it's heated or cooled. The relevant vector field for this example's the velocity of the moving air at a point. If air's heated in a region it'll expand in all directions such that the velocity field points outward from that region. Therefore the divergence of the velocity field in that… (More on Divergence)