from: Mc Graw Hill - 1999 - Perry - Chemical engineers handbook (VII Edition)
In monitoring a moving threadline, one criterion of quality would be the frequency of broken filaments. These can be identified as they occur through the threadline by a broken filament detector mounted adjacent to the threadline. In this context, the random occurences of broken filaments can be modeled by the Poisson distribution. This is called a Poisson process and corresponds to a probalistic description of the frequency of defects or, in general, what are called arrivals at points on a continous line or in time.