For the case of " extinction " (Bouguer), the sum of absorption and scatter, the terms absorption, scattering, and extinction cross-sections are often used. The fraction of light extinguished by the sample may be described by the extinction cross section (fraction extinguished per particle). the number of particles in a unit distance and the distance in those units. For example: [ (fraction extinguished / particle) (# particles / meter) (# meters / sample) = fraction extinguished / sample ]