What is organizational communication? Describe the formal and informal communication networks

Organizational communication is communication that occurs with an organizational context. Regardless of your career or level within an organization, your ability to communicate will affect not only the success of the organization but also your personal success and advancement within that organization.
Communication occurs in a variety of ways within an organization. Some communication flows are planned and structured; others are not. Some communication flows can be formally depicted, whereas some defy description.
Communication within an organization involves both formal and informal networks.
Formal communication network: This channel is typified by the formal organization chart, which is created by management to define individual and group relationships and to specify lines of responsibility. Essentially, the formal system is dictated by the managerial, technical, cultural, and structural environment of the organization. Within this system, people are required to behave and to communicate in certain ways simply to get work done. When employees rely almost entirely on the formal communication system as a guide to behavior, the system might be identified as a bureaucracy. Procedures manuals, job descriptions, organization charts, and other written materials dictate the required behavior. Communication channels are followed strictly, and red tape is abundant. Procedures are generally followed exactly; terms such as rules and policies serve as sufficient reasons for actions.
Informal communication network: This network, which is commonly called "the grapevine," continuously develops as people interact within the formal system to accommodate their social and psychological needs. Because the informal network undergoes continual changes and does not parallel the organizational chart, it cannot be depicted accurately by any graphic means. As people talk casually during breaks, text one another, or chat online, the focus usually shifts from topic to topic. One of the usual topics is work-job, company, supervisor, fellow employees. Even though the formal system includes definite communication channels, the grapevine tends to develop and operate within all organizations.