What actually is scattering?
In classical mechanics, the basic scattering process is illustrated with two billiard balls hitting each other. It is called a scattering because there is a change of direction and a transfer of energy.
In light scattering it is the change in direction of the energy that the light carries, an extension of the classical mechanics concept.
Light scattering is a form of scattering in which light in the form of propagating energy is scattered. Light scattering can be thought of as the deflection of a ray from a straight path, for example by irregularities in the propagation medium, particles, or in the interface between two media. Deviations from the law of reflection due to irregularities on a surface are also usually considered to be a form of scattering. When these irregularities are considered to be random and dense enough that their individual effects average out, this kind of scattered reflection is commonly referred to as diffuse reflection.
In quantum mechanics the scattering of particles from each other and off fields is described by quantum mechanical equations, where only the probability distribution of the scattered products can be calculated and checked against measurements. For example the quantum mechanical of photon off a nucleus. Feynman diagrams help in these calculations.