An open door policy means, literally, that every manager's door is open to every employee. The purpose of an open door policy is to encourage open communication, feedback, and discussion about any matter of importance to an employee. When a company has this policy, employees are free to talk with any manager at any time.
Companies adopt an open door policy to develop employee trust and to make certain that important information and feedback reach managers who can utilize the information to make changes in the workplace. An open door policy is normally a part of the employee handbook.
More About an Open Door Policy
Here is a Sample Open Door Policy.
Here's how an open door policy is supposed to work.