General Vollversammlung, I do not have any reference link though, but I know the usage in the practice.

The grapevine within an organization could be defined as an informal communication network supplementing official channels. People either having casual or informal department conversations at work. About 80 percent of the information on the grapevine pertains to business. Some executives are wary of the grapevine, possibly because it threatens their power to control the flow of information. Savvy managers tap into the grapevine, using it to spread and receive informal messages.