Broad Unicast is when you make multiple redundant unicast transmissions in order to deliver one piece of information to several recipients.

This is the wrong way to do it compared to multicast being the right way to do it.

We made the term up in our Jabber Enhancement Proposals as a better way to describe what XMPP does when the term broadcast is used. In XMPP terms it even means that redundant copies are transmitted when several of the recipients reside on the same machine.

But there are also many many other Internet applications which out of simplicity are using such a distribution approach, and therefore have a scalability issue.