Grapevine transmissions are a form of communication that involves the passing of information through informal channels, such as gossip and rumors. This type of communication is often used to spread news quickly, but it can also be unreliable due to the lack of verification of the source. The term 'grapevine transmissions' is often used interchangeably with the term 'rumors, ' which is a 6-letter word that can be used to describe this type of communication.