Operations research is a discipline that deals with the development and application of advanced analytical methodologies to provide decision support to complex decision-making problems in business, industry, government, and other enterprises. It encompasses a wide range of problem-solving techniques and methods such as data analysis, data mining, decision analysis, economic analysis and modeling, mathematical optimization, Markov decision processes, predictive analytics, probability theory, queueing theory, simulation, and statistics.
The following reference is to a paper that nicely details the origin of operations research:
McCloskey, J. F. (1987). The Beginnings of Operations Research: 1934-1941. Operations Research, 35(1), 143–152. http://www.jstor.org/stable/170920
Daniel M. Packer 