What is the difference between broadcast and gossip/epidemics?
While sometimes used as synonyms, to me, gossiping protocols are certain flavor of broadcast algorithms, where the message is flooded in a non-structural (commonly, random) way and spreads to the network.
In contrast, a non-gossiping broadcast algorithm may, for instance, deliver the message via a (predetermined) spanning tree, rather than let the message spread arbitrarily.
See, e.g., https://www.gsd.inesc-id.pt/~ler/reports/joaoleitaomsc.pdf