In general, scattering is what happens when light is forced to deviate from a straight path, or forced to deviate from a reflection angle described by the law of reflection. For example, in the X-ray region, atoms can scatter the X-rays in a well defined pattern. This is used to figure out the crystal structure of materials. Most of the visible light that humans see is from scattering. If scattering happens without energy loss (meaning the light only changes direction and the wavelength remains the same), it is called elastic scattering. If scattering happens with energy loss (meaning direction and wavelength change), it is called inelastic scattering. Raman scattering is a type of inelastic scattering.
