An informal organization is the whole of relationships, processes, information and decisions that take place outside the organizational structure of the formal organization. The informal organization is naturally created by personal sympathies and antipathies, organizational weaknesses, lack of leadership capabilities, or even rejection of official norms or goals.
Instead of attempting to rationalize organizations, Hawthorne experiments included a reversal. Organizational optimization did not take people into consideration, but these experiments revealed the importance of the informal organization for, among other things, the motivation of employees.
wiki
