More technically, the divergence represents the volume density of the outward flux of a vector field from an infinitesimal volume around a given point. ... While air is heated in a region, it expands in all directions, and thus the velocity field points outward from that region.

What is the significance of divergence?

Divergence measures the net flow of fluid out of (i.e., diverging from) a given point. If fluid is instead flowing into that point, the divergence will be negative. is often referred to as a "source" (of fluid, or whatever the field is describing), while a point or region with negative divergence is a "sink".

What does divergence and curl represent?

Roughly speaking, divergence measures the tendency of the fluid to collect or disperse at a point, and curl measures the tendency of the fluid to swirl around the point. Divergence is a scalar, that is, a single number, while curl is itself a vector.