Col John Boyd, USAF (Ret), coined the term and developed the concept of the OODA Loop: Observation, Orientation, Decision, Action

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Boyd’s complete OODA Loop presentation

“Knowledge of the strategic environment is the first priority.  Secondly, one must be able to interact with the environment and those within it appropriately.  You must be able to observe and orient yourself in such a way that you can indeed survive and prosper by shaping the environment where possible to your own ends, by adapting to it where you must.  Doing so requires a complex set of relationships that involve both isolation and interaction.  Knowing when each is appropriate is critical to your success.  In OODA Loop fashion, one must continually observe, orient, decide and act in order to achieve and maintain freedom of action and maximize the chances for survival and prosperity.  One does so through a combination of rapidity, variety, harmony, and initiative. It is these that are the core of "Boyd’s Way."  Rapidity of action or reaction is required to maintain or regain initiative.  Variety is required so one is not predictable, so there is no pattern recognition for a foe to allow him to know of your actions in advance and thus plan to defeat them.  Harmony is the fit with the environment and others operating in it.  Initiative – taking charge of your own destiny – is required if one is to master circumstances rather than be mastered by them.  All of course, would be focused on attaining the specified Objective that is implicit in this discussion.”  (The Essential Boyd by Grant T. Hammond)