10 Definitions Operations research, first called operational re­ search by P. M. S. Blackett (1) in Britain about 1938, has a broad zneaning illustrated by several exaznples in this section. Briefly, it znay be defined as the study of znan­ znachine systezns that have a purpose. In znore descriptive terzns, operations research involves the application of physical, biological, and social sciences in the znost quanti­ tative way possible. It thus draws on the disciplines of znedicine, psychology, and all forzns of engineering (2). As the following historical exaznples will show, an essential step in every 0 - R study is recognition of the purpose of an ope ration, an organiz ation, or a systezn. This often leads to a zneasure of znerit or a value parazneter by which operational results can be coznpared, for exaznple, the fraction of approaching aircraft shot down by an air-defense systezn, or annual sales of products by an industrial con­ cern, or gross national product of a country. Predictions of such operational results, and quanti­ tative coznparisons between different systezns, require znatheznatical znodels of each systezn and its operation. In sozne cases--such as the accuracy of anti-aircraft fire, or the cost of producing a znachined product, or transportation costs of delivery--the znodel can be znatheznatically precise or deterzninistic. More generally, operational results are probabalistic and require a stochastic znodel.