An approximation of a filter's ability to remove particles of a certain size or larger. Often does not perform at this level until a filter bed of particles builds up on the upstream side of the filter
George E. King Engineering, 5000 Oilfield Terms: A Glossary of Petroleum Engineering Terms, Abbreviations and Acronyms, US 2010. http://gekengineering.com/Downloads/Free_Downloads /Glossary_of_Petroleum_Engineering_Terms_25_August _2010.pdf, (Oil - Amer) {593}