The scattering intensity is the amount of radiation (e.g. x-ray or neutron) scattered at any particular angle. This quantity is usually given by , where q is the momentum transfer (a vector in reciprocal-space).
The form factor describes the shape of scattering objects, whereas the structure factor describes the organization of these objects (disordered, in a lattice, etc.). The scattering intensity, , is what is measured experimentally on a detector (including a possible background). However, this quantify is frequently converted into (or treated as), or , in order to perform further analysis.