Differential (scattering) cross section
From AMS Glossary
differential (scattering) cross section
A specification of the angular distribution of the electromagnetic energy scattered by a particle or a scattering medium.
The differential (scattering) cross section is defined as the ratio of the intensity of radiant energy scattered in a given direction to the incident irradiance and thus has dimensions of area per unit solid angle. The symbol σ is frequently used for scattering cross section and dσ/dΩ for the differential cross section.