Grapevine communication is an informal communication system where people share information without official lines of communication. It spreads like a grapevine through word of mouth gossip and rumors. Some key points about grapevines are that 40% of company information is shared through it, with 45% being shared before official announcements. It is not controlled by management but is highly believed by employees. Grapevines allow for very rapid sharing of information but can distort the original message and are not reliable. While they unite employees and fill communication gaps, grapevines can damage company reputation and productivity if not managed properly.