A gossip protocol is a highly effective, well established way of getting information to be quickly spread through a network. In essence any Node that receives a new piece of information, tells two (or more) neighbouring nodes about it. They then tell two or more each (2*2) and so on. This follows an exponential pattern until all Nodes in the network have been told.
This is how Radix ensures any new transactions are quickly shared with all relevant nodes in a highly reliable, fast and fault tolerant way.