Operational research (OR) is defined as a systematic and analytical approach to decision-making and problem-solving. It uses techniques from mathematics, statistics, and other fields to arrive at optimal or near-optimal solutions to complex problems. Some key points made in the document include: OR aims to help executives make better decisions; it follows a scientific approach and uses interdisciplinary teams; it considers the system as a whole and aims to find the best objective solution. OR has wide applications in fields like national planning, defense, industry, R&D, and agriculture. The OR modeling process typically involves 7 phases: problem formulation, system observation, model formulation, model verification, alternative selection, presentation of results, and implementation/evaluation.