A plan is typically any diagram or list of steps with details of timing and resources, used to achieve an objective to do something.
More formal plans as used for business and military purposes, while initially created with and as an abstract thought, are likely to be written down, drawn up or otherwise stored in a form that is accessible to multiple people across time and space.
It has not acquired a technical meaning, however, to cover the area of government legislation and regulations elated to the use of resources.
Planners are the professionals that have the requisite training to take or make decisions that will help or balance the society in order to have a functional, aesthetic, and convenient environment.
The subject touches such broad fields as psychology, game theory, communications and information theory, which inform the planning methods that people seek to use and refine; as well as logic and science (i.e. methodological naturalism) which serve as a means of testing different parts of a plan for reliability or consistency.