“Gossip is a peer-to-peer communication protocol in which nodes periodically exchange state information about themselves and about other nodes they know about. The gossip process runs every second and exchanges state messages with up to three other nodes in the cluster. The nodes exchange information about themselves and about the other nodes that they have gossiped about, so all nodes quickly learn about all other nodes in the cluster. A gossip message has a version associated with it, so that during a gossip exchange, older information is overwritten with the most current state for a particular node.” Cassandra
A blockchain is made of network nodes and they have to communicate somehow. The Gossip Protocol is widely used for this purpose. It communicates block and transaction level information to peers. It is an example of a p2p network protocol.
Gossip protocols are eventually consistent using an epidemiological protocol. The analogy is to how epidemics spread via nearest neighbours; information is broadcast in the same fashion by networks using gossip.
The messages under gossip are sent to gossip partners and hence a probablistic outcome is determined.
Demer had also proposed a distance based protocol under gossip.