What are Core Updates?
Core Updates, aka ‘Broad Core Updates’ or ‘Core Algorithm Updates’, are Google algorithm updates which are more significant than other smaller incremental updates.
Google says Core Updates should be more ‘noticeable’, and made only ‘several times a year’.
Core Updates should usually be announced by Google via communication channels such as the SearchLiason account on Twitter and/or the Google Search Central blog.
How often do Core Updates happen?
According to Google’s documentation Core Updates should happen every few months, though they could happen more, or less frequently than this.
Broad core updates tend to happen every few months.
Google Search Blog
List of Google updates
Google have an official list of search ranking updates that you can find here.
The list currently starts at January 13, 2020.