The meaning of the term divergence can be at least partially understood from Figure 2.15a where the source in Figure 2.14 is shown again, but now we take a small volume around the source itself. Again using the analogy of water, the flow is outward only. This indicates that there is a net flow out of the volume through the closed surface. Moreover, the flow “diverges” from the point outward. We must, however, be careful with this description because divergence does not necessarily imply as clear a picture as this. The flow in Figure 2.15b has nonzero divergence as well even though it does not “look” divergent. A simple visual picture of divergence is a jet engine. Enclosing the engine by an imaginary surface indicates a net flow outward.
: