Informal Organization

Definition: the Informal Organization is the connecting social structure in organizations that denotes the constantly evolving network of social interactions among its employees, unrelated to the firm's formal authority structure.
It is a dynamic aggregate of the personal, professional and social relationships, communities and social networks that arise spontaneously as people relate with one another in the work environment.
The IO compliments the formal organization and makes it more effective by providing additional communication channels, improving operational agility (responsiveness), fostering innovation, and enabling better collaboration.

More on the informal organization. More on organizational structure: Formal Organization, Organization Chart, Rendanheyi Model, Reorganization, Structural Integration.