John Mueller of Google was asked if there is a difference between a Google broad core update and a Google core update. John responded on Twitter "I imagine that's generally the same." I suspect they are.
Here is the question and answer:
I imagine that's generally the same (though I don't really know where you're getting them from).
— 🍌 John 🍌 (@JohnMu) February 18, 2020
From how I see it, they are the same. The "broad" part is when Google announces the core updates, like every few months. Google does probably smaller core updates between them. But the "broad" core update is a bigger one that Google generally has been doing every quarter or so.
I can be wrong - but this is how I understand the difference between them. Although, Google internally might not differentiate them this way or call them by these names.
Forum discussion at Twitter.
Update: Glenn Gabe references an old mention of this:
Google said that there were "several core ranking changes" when referring to the November 8th volatility. Not a broad core update, but core ranking changes. So yes, there's a difference. :) https://t.co/LU1VUXptar
— Glenn Gabe (@glenngabe) February 19, 2020