A point source of pollution is a single identifiable localized source of air, water, thermal, noise or light pollution. A point source has negligible extent, distinguishing it from other pollution source geometries. The sources are called point sources because in mathematical modeling, they can be approximated as a mathematical point to simplify analysis. Water pollution from an oil refinery wastewater discharge outlet is an example of point source water pollution.
For more, visit the Wikipedia entry for point source pollution, URL: http://en.wikipedia.org/wiki/Point_source_pollution