Explanation:

- Horizontal Communication

- Refers to communication between employees or departments at the same hierarchical level.

- Enhances coordination and collaboration across teams.

- It is part of the formal communication channels.

- Formal Communication

- Involves official and structured channels within an organization.

- Includes emails, memos, and reports.

- Typically flows in hierarchical patterns.

- Grapevine

- Refers to informal channels of communication in an organization.

- Spreads unofficial or informal information among employees.

- Can sometimes lead to rumors but also facilitates workplace culture.

- Gang Plank

- A concept introduced by Henri Fayol to describe bypassing the formal chain of command to communicate.

- Encourages direct communication for urgent matters.

- Not an informal channel itself, but a method to expedite communication.