Thomson scattering is the result of a collision between a photon (an electromagnetic wave) and a charged particle, such as an electron. When an electron and photon "collide" the electron feels a Lorentz force from the oscillating electric and magnetic fields of the photon and is accelerated. This acceleration causes the electron to emit a different photon in a different direction. This emitted photon has a wavelength shifted from that of the incident photon by an amount dependent on the electron energy. Another way of looking at this is that the electron absorbs the energy of the photon and re emits the energy in the form of a different electromagnetic wave. This scattering of a photon by an electron is called Thomson Scattering.